Vyborg's most prominent landmark is the Swedish built castle, started in the 13th century and extensively reconstructed in 1891–1894. The Round Tower and the Rathaus Tower date from the mid-16th century. The Viipuri Library by Finnish architect Alvar Aalto is a reference point in the history of modern architecture.
There are also Russian fortifications, completed by 1740, as well as the monuments to Peter I (1910) and Torkel Knutsson. Tourists can also visit the house where the Russian revolutionary Vladimir Lenin prepared the Bolshevik revolution during his stay in Viipuri from 24 September to 7 October 1917.
Sprawling along the heights adjacent to the Gulf of Finland is Mon Repos, one of the most spacious English parks in Eastern Europe. The park was laid out on behest of its owner, Baron Ludwig Heinrich von Nikolay, at the turn of the 19th century. Most of the garden structures were designed by the architect Giuseppe Antonio Martinelli. Previously, the estate belonged to the future king Frederick I of Württemberg (Maria Fyodorovna's brother), who called it Charlottendahl in honor of his second wife.