Karosta prison is something completely different from the usual sightseeing. It gives you an insight in the Latvian history when Latvia was part of the USSR. So I learned that the Karosta naval base in Sovjet times was kept very secret, even the Karosta Canal was never mentioned on the maps. My guide in the prison knew a lot of the history, spoke excellent English and i could ask loads of questions. So well worth a visit. And after your visit, take a walk around the old navel base. There are a lot of abandoned, derelict but still beautiful buildings. Empty now for more then a decade since the Russians left the naval base.