Yes! I was actually looking for Monrepos, the interesting park in which the mausoleum and the island (Ludwigstein) are located in. The park has been something of travel destination in Finland, but then the city of Vyborg was conquered by the Soviets and the entire population fled west to what is Finland today. The whole park (and one could say the city itself) fell into horrible disrepair during communism, but in the last ten years or so Russia has renovated the park, partly with World Bank funding.
https://en.wikipedia.org/wiki/Monrepos_Park
Thank you Morty for the color commentary and links for the Monrepos research center in Germany! You inspired me to put this up, but I did not want to comment it until both Monrepos are guessed right. Loli is up!