Although the city of Sortavala itself is a pleasant city on the shore of Lake Ladoga with a distinct Finnish influence, most tourists come to this city to experience three sights outside the city: the Ruskeala Mountain park that was created around an abandoned marble mine, the Ladoga Skerries - an archipelago consisting of small rocky islands - and the island and monastery of Valaam. Sortavala can be reached via St Petersburg.
Note that Sortavala and especially Ruskeala are considered part of Russia’s border territory and so your may be asked by border guards or even FSB officials to show your documents and explain your reason for visiting.