Built or owned by the Swiss:
I am never quite sure if we allow buildings "designed by" as equivalent to "Built by" under this Connection.
Never mind - Domenico Trezzini from Astano in the Ticino designed large parts of St Petersburg for Peter the Great - some of which are definitely still standing! See http://www.saint-petersburg.com/italian/domenico-trezzini/
One of the houses he designed, is now a boutique hotel called "The Trezzini Palace". Its history is here but only in Russian. http://trezzinipalace.com/istoriya-otelya
If my understanding of the Google translation is correct it was granted to his descendents (his son was also an architect who worked in St Petersburg) and he may even have lived in it for a short period before his death.
There was also another Swiss Trezzini who worked in St Petersburg - Pietro Antonio Trezzini https://en.wikipedia.org/wiki/Pietro_Antonio_Trezzini
. Indeed it appears that a number of Swiss architects went to St Petersburg -see this article by the Swiss Dept of Foreign Affairs - http://www.swissworld.org/en/culture/st_petersburg/architects/
But I can find nothing about their "ownership" of any property there
Enough to go with??