Olsztyn (UK: /ˈɒlʃtɪn/ OL-shtin,[2] Polish: [ˈɔlʂtɨn] ⓘ; German: Allenstein [ˈʔalənʃtaɪn] ⓘ; Old Prussian: Alnāsteini [a]) is a city on the Łyna River in northern Poland.

Today, the Castle of Warmian Cathedral Chapter houses a museum and is a venue for concerts, art exhibitions, film shows and other cultural events, which make Olsztyn a popular tourist destination.

[16] The city was sacked by Swedish troops later, in 1655 and 1708, during the next Polish-Swedish wars, and its population was nearly wiped out in 1710 by epidemics of the bubonic plague and cholera.

Napoleon gathered enormous forces in the city and planned to engage the Russians and Prussians in a decisive battle.

Thanks to the victory at Allenstein, Napoleon's army was able to move north and a few days later the general Battle of Eylau took place.

[20] In the early 1830s the city suffered from a cholera epidemic and a hunger crisis, however afterwards it flourished again, when despite Germanisation policies it was administered by Polish mayor Jakub Rarkowski from 1836 to 1865.

[17] Allenstein's infrastructure developed[23] rapidly: gas was installed in 1890, telephones in 1892, public water supply in 1898, and electricity in 1907.

Shortly after the outbreak of World War I in 1914, Russian troops captured Allenstein, but it was recovered by the Imperial German Army in the Battle of Tannenberg.

[16] In March, Polish activist Bogumił Linka died in Allenstein, a few weeks after being attacked by the German militia in nearby Szczytno in Masuria.

[16] In the interwar period, numerous Polish organisations operated in the city, including the Polish Scouting and Guiding Association, Union of Poles in Germany, a People's Bank (Bank Ludowy),[10] local Poles organised a school, library, puppet theatre.

[31] In August 1939, Germany introduced martial law in the region, which allowed for even more blatant persecution of Poles.

[34] Nazi Germany co-formed the Einsatzgruppe V in the city, which then entered several Polish cities and towns, including Grudziądz, Mława, Ciechanów, Łomża and Siedlce, to commit various atrocities against Poles during the German invasion of Poland that began World War II in 1939.

Arrested Poles were held in a local prison and then forced to remove Polish signs and inscriptions in the city, while the German population gathered and insulted them.

[37] The Gazeta Olsztyńska was abolished by the German authorities, the newspaper's headquarters was demolished and the editor-in-chief Seweryn Pieniężny was arrested and executed in the Hohenbruch concentration camp [de][16][36] along with co-publisher Wojciech Gałęziewski and the "Rolnik" Cooperative chief Leon Włodarczyk, while Pieniężny's wife was deported to the Ravensbrück concentration camp.

As part of the Aktion T4, Nazi Germany conducted medical experiments on the patients of the psychiatric hospital in the present-day district of Kortowo, in which at least 5,000 people were killed.

[41] On 22 January 1945, near the end of the war, the city was plundered and burned by the conquering Soviet Red Army, and much of its German population fled.

[41] Remains of three Roman Catholic nuns who served as nurses at Olsztyn's St. Mary's Hospital and were killed by Soviet soldiers in 1945 were excavated in October 2020.

In October 1945, the remaining German population was expelled in accordance with the Potsdam Agreement, and remaining Poles were joined by new Polish settlers,[46] mostly those expelled from pre-war Polish regions of Vilnius, Grodno and Volhynia, annexed by the Soviet Union, as well as settlers from Warsaw, which had been destroyed by German forces during World War II.

In December 1945, a match factory was launched in Olsztyn, as the city's first post-war industrial plant of national importance.

Access to the castle leads from the drawbridge over the river Łyna, surrounded by a belt of defensive walls and a moat.

[50] In the sixteenth century, there were two prince-bishops of Warmia that stayed there: Johannes Dantiscus – the first Sarmatian poet, endowed with the imperial laurel wreath for "Latin Songs" (1538, 1541) and Marcin Kromer, who wrote with equal ease in Latin and Polish scientific and literary works (1580).

After the Prussian annexation of Warmia during the First Partition of Poland in 1772, the castle became the property of the state board of estates (Kriegs- und Domänenkammer — War and Domain Chamber).

In addition, there are also popular events held within the frameworks of the Olsztyn Artistic Summer and so-called "evenings of the castle" and "Sundays in the Museum".

Municipal greenery (560 ha, 6.5% of the town area) developed in the form of numerous parks, green spots and three cemeteries over a century old.

The greenery includes 910 monuments of nature and groups of protected trees in the form of beech, oak, maple and lime-lined avenues.

The Michelin Polska tyre company (former Stomil Olsztyn) is the largest employer in the region of Warmia and Masuria.

[79] In 1939, due to poor economic situation throughout the interwar period and the city's growing population, a trolleybus line began operation, partially replacing the original tram network.

[83] In 2006, authorities considered the reintroduction of trams in the city to address transport problems and subsequently concluded feasibility studies on the matter in 2009.

[86] In 2024, a 6 kilometres (4 miles) long extension was completed the Turkish manufacturer Durmazlar had been selected to supply 24 trams for the network.

The main office of the federation is situated at Olsztyn Planetarium and Astronomical Observatory, located on St. Andrew's Hill (143 m) in a former water tower erected in 1897.