Darłowo (Polish pronunciation: [darˈwɔvɔ]; Kashubian: Dërłowò; German: Rügenwalde), is a seaside town in the West Pomeranian Region, at the south coast of the Baltic Sea, north-western Poland, with 13,324 inhabitants as of December 2021. It is located in Sławno County in West Pomeranian Voivodeship on the Slovincian Coast.

The earliest archaeological signs of a settlement in the area occurred when Roman merchants travelled along the Amber Road in the hope of trading precious metals like bronze and silver for amber. By the 11th century the location of the later town was already becoming a significant trading point. The settlement received its town rights in 1312. Over the years Dukes of Pomerania constructed a Ducal Castle called Dirlow on a nearby island and chose it as their seat.

It was here that the largest artillery piece in the world, Schwerer Gustav, was constructed and tested by Nazi Germany during World War II.

The original medieval outline of Darłowo has been preserved to this day. The Old Town, Ducal Castle and local beaches are popular among holidaymakers. Darłowo is also an important historical centre as it is the birthplace and burial site of Eric of Pomerania, King of Denmark, Sweden and Norway.

After the last Ice-age had ended at about 8000 BC, settlers of the Stone Age first populated the region. Around 100 AD the region of the later town was inhabited by the East Germanic tribe of the Rugii. According to Ptolemy at the site of the later city was a settlement called Rugium.

In the 10th century, the region became part of the emerging country of Poland under its first ruler Mieszko I. By the eleventh century a fortress named Dirlow, (or Dirlovo) existed where the River Wieprza entered the Baltic. From this fortress, the district of Dirlow was administered, which belonged to the castellany of Sławno. A town was later founded in the district of Dirlow, but not at the location of the fortress itself. Following Poland's fragmentation, it was at various times part of the western and eastern duchies of Pomerania.

The town was probably founded in 1270 by Vitslav II of the Danish Principality of Rügen, at that time also ruler of the Lands of Sławno and Słupsk. The first mention of the town is in a document of 5 February 1271. The settlement decayed.

The town was destroyed in 1283 during a conflict between Vitslav II and Mestwin II (Polish: Mszczuj or Mściwój). In a chronicle of 1652, Matthäus Merian stated that the town had been destroyed by Bogislaw of Pomerania, when after Mestwin's II death in December 1294 the Duke Przemysł II (future king) of Poland acquired the town, as a consequence of Treaty of Kępno.

In 1308, the town along with the coastal region of Poland was invaded and occupied by Brandenburg. The town was rebuilt and on 21 May 1312, it was granted Lübeck law under the administration of the noble brothers John, Peter, and Lawrence of the Swienca family, vassals of the Brandenburg margraves since 1308. The Brandenburg margraves undertook in 1308 a campaign against Gdańsk, Poland.

The town passed to the Duchy of Pomerania in 1347, at that time ruled by the brothers Bogislaw V, Wartislaw V, and Barnim IV of the House of Pomerania dynasty. Bogislaw, son-in-law of king Casimir III of Poland, would become ruler of the area after the partition of Pomerania-Wolgast in 1368. This part duchy was known as Pomerania-Stolp (Duchy of Słupsk). Duke Bogislaw VIII, a Polish vassal, tried to direct Polish Baltic trade to the Port of Darłowo, but without success.

In 1352 the construction of the castle began, and co-operation with the Hanseatic League was initiated, with the town becoming a full member of the organization in 1412. The town had its own trade fleet, larger than in other surrounding towns; it actively traded with Lübeck, while boats and ships owned by local merchants travelled as far as Normandy and Spain. In 1382 Eric of Pomerania, later the king of Norway, Denmark and Sweden, was born in the town. After losing his thrones, he returned to his birthplace and began to expand his duchy. After his death in 1459, he was buried in St. Mary's Church. After Eric's death, the town was ruled by Duke Eric II of Pomerania-Wolgast.

Another significant ruler was Bogislaw X (1454–1523) under whose administration sea trade with the Hanseatic League and land trade with Poland grew increasing the prosperity of the area.

The town suffered a series of natural disasters. In 1497 and 1552 the harbour of the town, known in German as Rügenwaldermünde, and parts of the town were hit by great storms. Ships which broke from their moorings were seen drifting in the vicinity of the town and of the neighbouring village of Suckow. In 1589, 1624, 1648, 1679 and 1722 fires damaged the town.

From 1569 to 1622, it was the capital of a small eponymous duchy, and afterwards it was again part of the Duchy of Pomerania. After the death of the last Pomeranian Duke Bogislaw XIV in 1637, the end of the contemporary Thirty Years' War in 1648 and the subsequent partition of the Duchy of Pomerania between the Swedish Empire and Brandenburg-Prussia in the Peace of Westphalia and the Treaty of Stettin (1653), Brandenburg included Farther Pomerania with Rügenwalde in her Pomeranian province. Following the annexation by Brandenburg the town entered a period of economic stagnation. The harbour of Rügenwaldermünde was destroyed during the Thirty Years' War by imperial troops, and was reconstructed by order of King Frederick II of Prussia not before 1772. The first lighthouse was built around the year 1715.

During the Napoleonic Wars some of Rügenwalde's inhabitants, in particular ship owners and businessmen, profited from smuggling British goods to the continent. In 1871 the town, along with Prussia, became a part of the German Empire. A railway reached the town in 1878, providing connections with Danzig (Gdańsk) and Stettin (Szczecin). It simultaneously became a popular health resort, mainly due to the exceptional climate. The Royal Swedish Vice Consulate was located in the town in 1859–1901 (Vice Consul Bertold August Riensberg, b. 1823) and in 1914–1936 (Vice Consul Albert Rubensohn, b. 1879).

In 1935 the German Army Firing Test Range Rügenwalde-Bad [de], designed for testing heavy guns, including long-range railway guns such as Krupp K5, was built between Rügenwalde's harbour Rügenwaldermünde and the village of Suckow. Some of the largest guns in military history were tested here: Schwerer Gustav and Mörser Karl. Gun barrels with a length of up to 47 metres (154 feet) were tested. For long-distance tests, target areas within the Baltic Sea North of Großmöllendorf and Henkenhagen (about 80 kilometres (50 miles) away from Rügenwaldermünde) and North of Dievenow and Swinemünde (120 to 130 kilometres (75–81 miles) away) were used. The test site was visited by high-ranking officers of the German Army, Air Force and Navy, including Admiral of the Fleet Erich Raeder and field marshals von Rundstedt, Wilhelm Keitel and Hermann Göring.

During World War II, the Germans operated a forced labour subcamp of the Stalag II-B prisoner-of-war camp for Allied POWs in the town.

During World War II Rügenwalde was used to house families made homeless after the Allied bombing of Hagen and Bochum in the Ruhr district. Shortly before the end of World War II, numerous German refugees from the provinces of East Prussia and Reichsgau Danzig-West Prussia arrived in the region. In early 1945, about 5,600 people escaped by ships of Operation Hannibal before Soviet Troops reached the town on 7 March 1945. About 3,500 citizens remained in the town or returned again after failing to escape.

Following the defeat of Nazi Germany, border changes promulgated at the Potsdam Conference assigned the town once again to Poland, and its German population was expelled. The first expulsion of the surviving German inhabitants took place on 17 October 1945, followed by a series of further expulsions beginning on 17 August 1946. In 1949 only about 70 Germans were left in the town. In 1946–47, the town was repopulated with Poles and Lemkos, who partly came from what had been eastern Poland but was annexed by the Soviet Union. The town was given the Polish name Dyrłów, and later Darłów, before changing to the current name.

The German name Rügenwalde was best known in Germany for the production of the Rügenwalder Teewurst in the town; after World War II the production was restarted in West Germany under the old name.

From 1950 to 1998, it was administratively located in the Koszalin Voivodeship.

Today the Polish Darłowo is a summer resort. A coast aquapark with desalinated seawater is available there, the only one in Poland.

The entire Old Town area in Darłowo has been entirely preserved. Darłowo has maintained the unique medieval urban planning with the main square in the middle of the town. During medieval times the town was surrounded by walls and had four gates; only one gate, Brama Wysoka (High Gate), has survived in a fairly original shape.

Although documents directly relating to the construction of the castle in Darłowo have not been found yet, the results of archaeological and architectural and historical premises allow us to date back the creation of the castle to the second half of the fourteenth century. It was during the reign of the prince of the House of Griffins, Boguslaw V and Elizabeth, the daughter of King Casimir the Great. The prince purchased the island with a mill in 1352 from a rich burgher of Darłowo – Elizabeth von Behr – in order to build a fortress on it. Over the decades, a castle had grown on the island, which in its main outlines has survived to this day. The work of Boguslaw V was at that time so representative that so that as early as in 1372 a congress of the Pomeranian princes – brothers and cousins Boguslaw took place within its walls. The first sovereign, who modernised the defence system and extended the castle was Prince Eric the Pomeranian. It took place in the years 1449 to 1459, when after the loss of the throne of Scandinavia, the dethroned king returned to his legacy.

An old king was accompanied by a beautiful and young servant-maid Cecilia, who was the love of his life. Historians still argue about who this mysterious woman really was. Some of them maintain that in the last years of his life, reaching his seventies – she became his wife. One of the contemporary chronicles mention her as "the queen Cecilia".

Shrouded in mystery, the history of the great love of King Eric and Cecilia became an inspiration for artists. The poem "The Return of the Prince Eric" was created by a poet and writer of Koszalin – Czeslaw Zea, and an American journalist and writer Lucie Lehmann – Barclay has been penetrating the archives of Denmark, Sweden, Norway, Germany and the UK for several years in search of traces of Cecilia and Eric. The aim of the writer is to create a love novel of this unique pair based on historical facts. The initial appearance of a medieval fortress of Darłowo was an inspiration to build a similar but larger Kronborg Castle by King Erik in Denmark, where after years, William Shakespeare placed the action of "Hamlet".

The castle of Darłowo is also associated with the figure of Eric Pomerania's granddaughter – Princess Sophia. Legend attributes to her, apparently contrary to the historical facts, cruelty, for which she lingers as the White Lady after her death, circling the castle. The character of Princess Sophia is also related to a romantic love story. The lady of the Darłowo castle was to bestow John of Maszewo with great reciprocating feeling. His Gothic tenement still stands today on the corner of the streets of Powstańców Warszawskich and Morska. Supposedly, the ducal castle was connected with the house of the knight with a secret underground passage, which the knight used at night to sneak into his Lady's... The historical novel based on the life of Princess Sophia, entitled "Beautiful Princess", was written by a writer Zbysław Gorecki living in Darłowo for many years. In the Prussian times, the castle served partly as a warehouse and fell into ruin. Only at the end of the 1930s, a regional museum was created there and it is operating. Its founder and first curator was Karl Rosenow.

Today the castle serves as a Polish Museum. The castle is built in gothic style on a base plan resembling a square; its tower is 24 metres (79 feet) high. This is the only castle of such characteristic on the Polish seacoast.

The peculiarity of Darłowo museum is a two-headed calf, which was probably born in the village Janiewice, district of Sławno in 1919. Another interesting feature of the castle is a cat mummy and a golden sculpture of a dove – a talisman of luck for King Eric and Cecilia. Since the autumn of 2010, a statue of King Eric, showing the "king of exile" has been standing in the courtyard, funded by the Baltic Cooperative Bank in Darłowo.