Tsar Nicholas I established the Patarei sea fortress which then worked as an artillery battery. The buildings on four hectare have had many different functions: barracks, prison and since 2007 a culture park. 
You can visit the former sea fortress rebuilt into a prison until September. The doors are open every day from 12 pm to 7 pm. Tickets cost 2 Euros. 
As an occupants of the prison you needn't worry about hunger or thirst. The prison shop and café will cater for you.
Patarei sea fortress and prison is situated in leafy Kalamaja area at Kalaranna 2. 
More information from: Patarei Sea Fortress