Question: Which major Russian city borders the body of water that contains Ertholmene?

full_context: Document 1: Christiansø Lighthouse: Christiansø Lighthouse () is located on the top of the Store Tårn tower on the Danish island of Christiansø, some northeast of Bornholm in the Baltic Sea. Constructed and brought into service in 1805, it is one of Denmark's oldest.
Document 2: Japanese Lighthouse (Poluwat, Chuuk): The Japanese Lighthouse, or Poluwat Lighthouse, is an abandoned lighthouse situated on Alet Island in Poluwat, Chuuk in the Federated States of Micronesia. It was completed in 1940 by the Japanese and was in use until being attacked by U.S. forces in World War II. It was listed on the National Register of Historic Places in 1983. The lighthouse is a good example of pre-World War II "marine architecture" built by the Japanese.
Document 3: Torbjørnskjær Lighthouse: Torbjørnskjær Lighthouse (, ) is a fully automated coastal lighthouse situated on a skerry in the archipelago municipality of Hvaler, Norway. It marks the east side of the entrance to the Oslofjord, with Færder marking the west. The light is powered by solar power. Landing conditions are very difficult, and nowadays service calls are made via helicopter. The lighthouse and surrounding buildings, which include residences, outhouse, a well, and engine house are proposed protected as a national park.
Document 4: Heggholmen Lighthouse: Heggholmen Lighthouse () is a coastal lighthouse located in the Oslofjord, in the municipality of Oslo, Norway. It was established in 1827, and automated in 1972. The lighthouse was listed as a protected site in 1998.
Document 5: Baltic Sea: Since May 2004, with the accession of the Baltic states and Poland, the Baltic Sea has been almost entirely surrounded by countries of the European Union (EU). The only remaining non-EU shore areas are Russian: the Saint Petersburg area and the exclave of the Kaliningrad Oblast.
Document 6: British Isles: Ireland and the United Kingdom are both part of the European Union (EU). The Crown Dependencies are not a part of the EU however do participate in certain aspects that were negotiated as a part of the UK's accession to the EU. Neither the United Kingdom or Ireland are part of the Schengen area, that allow passport-free travel between EU members states. However, since the partition of Ireland, an informal free-travel area had existed across the region. In 1997, this area required formal recognition during the course of negotiations for the Amsterdam Treaty of the European Union and is now known as the Common Travel Area.
Document 7: Thunder Bay Island Light: Thunder Bay Island Light, located on Thunder Bay Island's southeast tip, is one of the oldest operating lighthouses in Michigan. The third operating U.S. lighthouse in Lake Huron was built here in 1831, but it disintegrated almost at once and was rebuilt in 1832 of local limestone. This 1830s light tower was raised ) to a height of in 1857, and sheathed with brick. A fourth order Fresnel lens was installed. This 1857 light tower is the current Thunder Bay Island Light, although the tower has been further altered and is currently high.
Document 8: Baltic region: The terms Baltic region, Baltic Rim countries (or simply Baltic Rim), and the Baltic Sea countries refer to slightly different combinations of countries in the general area surrounding the Baltic Sea in Northern Europe.
Document 9: South Stack Lighthouse: The lighthouse has warned passing ships of the treacherous rock below since its completion in 1809. The -tall lighthouse on South Stack was designed by Daniel Alexander and the main light is visible to passing vessels for , and was designed to allow safe passage for ships on the treacherous Dublin–Holyhead–Liverpool sea route. It provides the first beacon along the northern coast of Anglesey for east-bound ships. It is followed by lighthouses, fog horns and other markers at North Stack, Holyhead Breakwater, The Skerries, the Mice, Point Lynas and at the south-east tip of the island Trwyn Du. The lighthouse is operated remotely by Trinity House. It has been visited by the team at "Most Haunted".
Document 10: Estonia: Estonia (i/ɛˈstoʊniə/; Estonian: Eesti [ˈeːsti]), officially the Republic of Estonia (Estonian: Eesti Vabariik), is a country in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia (343 km), and to the east by Lake Peipus and Russia (338.6 km). Across the Baltic Sea lies Sweden in the west and Finland in the north. The territory of Estonia consists of a mainland and 2,222 islands and islets in the Baltic Sea, covering 45,339 km2 (17,505 sq mi) of land, and is influenced by a humid continental climate.
Document 11: Latvia: Latvia ( or ; , ), officially the Republic of Latvia (, ), is a country in the Baltic region of Northern Europe. Since its independence, Latvia has been referred to as one of the Baltic states. It is bordered by Estonia to the north, Lithuania to the south, Russia to the east, and Belarus to the southeast, and shares a maritime border with Sweden to the west. Latvia has 1,957,200 inhabitants and a territory of . The country has a temperate seasonal climate.
Document 12: North Cape Light: The North Cape Light is an active lighthouse on Prince Edward Island, Canada. It was built in 1867, and is still active.
Document 13: Poland: Poland is bordered by the Baltic Sea, Lithuania, and Russia's Kaliningrad Oblast to the north, Belarus and Ukraine to the east, Slovakia and the Czech Republic to the south, and Germany to the west.
Document 14: Kaliningrad: Kaliningrad (Russian: Калининград, IPA: (kəljɪnjɪnˈɡrat); former German name: Königsberg; Yiddish: קעניגסבערג, Kenigsberg; Russian: Кёнигсберг, tr. Kyonigsberg; Old Prussian: Twangste, Kunnegsgarbs, Knigsberg) is the administrative center of Kaliningrad Oblast, a Russian exclave between Poland and Lithuania on the Baltic Sea.
Document 15: Lågskär Lighthouse: Lågskär Lighthouse is an automated lighthouse located on the north side of Lågskär, one of Finland's Åland Islands in the Sea of Åland of the Baltic. It is the only striking feature on Lågskär on the generally uninhabited island.
ground_truth: Saint Petersburg
sub_queries: Ertholmene >> located on terrain feature Answer: Baltic Sea
which major russian city borders Baltic Sea Answer: Saint Petersburg