The ruin of Hammershus, at the northwestern tip of the island, is the largest medieval fortress in northern Europe, testament to the importance of its location.

Bornholm and Ertholmene comprise the last remaining Danish territory in Skåneland east of Øresund, having been surrendered to Sweden in 1658, but regained by Denmark in 1660 after a local revolt.

The island's topography consists of dramatic rock formations in the north (unlike the rest of Denmark, which is mostly gentle rolling hills) sloping down towards pine and deciduous forests (greatly affected by storms in the 1950s), farmland in the middle and sandy beaches in the south.

Occupying an area of 584.59 square kilometres (225.71 sq mi),[2] the island had a total population of 39,332 as of January 2024[update].

After the war in 1658, Denmark ceded the island to Sweden under the Treaty of Roskilde along with the rest of the Skåneland, Bohuslän and Trøndelag, and it was occupied by Swedish forces.

A revolt broke out the same year, culminating in Villum Clausen's shooting of the Swedish commander Johan Printzensköld on 8 December 1658.

In addition to Oluf Høst, they include Karl Isaksson (1878–1922) from Sweden, and the Danes Edvard Weie (1879–1943), Olaf Rude (1886–1957), Niels Lergaard (1893–1982), and Kræsten Iversen (1886–1955).

The wreckage was photographed and sketched by the Danish Naval Officer-in-Charge on Bornholm, Lieutenant Commander Hasager Christiansen.

[9] During the Soviet bombing of the two main towns on 7-8 May 1945, Danish radio was not allowed to broadcast the news because it was thought it would spoil the liberation festivities in Denmark.

[10] On 9 May, Soviet troops landed on the island, and after a short fight, the German garrison (about 12,000 strong[11]) surrendered.

[13] Later research found that the Soviet bombing of Bornholm resulted in approximately three thousand Danish civilians in Rønne becoming homeless, while damaging a majority of the houses in Nexø, fully destroying roughly one-tenth.

Ten Danes were killed and thirty-five wounded, considered a low number, owing to the fact that many civilians were evacuated to shelters on the outskirts of the respective towns before the worst raids hit.

[17] On 5 March 1953, the day of Stalin's death, Polish pilot Franciszek Jarecki defected from the Eastern Bloc and landed a MiG-15 fighter on the island.

[18] In 2017, Denmark's Defence Intelligence Service decided to build a listening tower near Østermarie, almost 90 meters high, to intercept radio communications across the Baltic Sea and in parts of Russia.

It is the result of a merger of the five former (1 April 1970 until 2002) municipalities on the island (Allinge-Gudhjem, Hasle, Nexø, Rønne and Aakirkeby) and the former Bornholm County.

From 1 January 2007 all counties were abolished, and Bornholm became part of the Capital Region of Denmark whose main responsibility is the health service.

From 1 January 2010 until 31 December 2020 the mayor was Winni Grosbøll, a high school teacher and a member of the Social Democrats (Socialdemokratiet) political party.

This was after an agreement (aftale om konstituering) between the Red-Green Alliance, amongst whom Morten Riis will be deputy mayor, and the Danish People's Party with the Conservatives.

Ferry services connect Rønne to Świnoujście (Poland), Sassnitz (Germany), Køge, 45 kilometres (28 miles) by road (34 kilometres or 21 miles as the crow flies) south of Copenhagen, Denmark; the destination to Køge replaced the nighttime route directly to and from Copenhagen (for both cargo and passengers) from 1 October 2004; and catamaran services to Ystad (Sweden).

There is however one exception, centrally placed Aakirkeby, which was also the name of the municipality from 1970 until 2002, but it included the harbour of Boderne, 5 kilometres (3.1 miles) to the south.

Other localities (with approximate populations, not updated) include Aarsballe (86), Arnager (151), Olsker (67), Rutsker (64), Rø (181), Stenseby (?)

The island's varied geography and seascapes attract visitors to its many beauty spots from the Hammeren promontory in the northwest to the Almindingen forest in the centre and the Dueodde beaches in the southeast.

Of special interest are the rocky sea cliffs at Jons Kapel and Helligdomsklipperne, the varied topography of Paradisbakkerne and rift valleys such as Ekkodalen and Døndalen.

[24] Furongian (late Cambrian period) sediments of the Alum Shale Formation of Bornholm presented by all six superzones; three agnostoid and fourteen trilobite zones are defined by fossils.

Described gerena include Ctenopyge, Eurycare, Leptoplastus, Olenus, Parabolina, Peltura, Protopeltura, Sphaerophthalmus, Lotagnostus and Triangulopyge.

[28] The ancient site of Rispebjerg has remains of sun temples from the Neolithic and earthworks from the Iron Age.

[35] Bornholm has an oceanic climate relatively similar to southern Sweden and mainland Denmark, whose summer highs and winter lows are heavily moderated by its maritime and isolated position.

The winter of 2010 – 2011 was exceptionally extreme with snow depth reaching at least 146 cm (58 inches) and snowdrifts of six meters (20 feet), the highest in Northern Europe.