Old Post Office, along with the park it is a typical design of H. Marconi from 1829. It used to be a horse changing station for sixteen horses, expedition and small hotel rooms for special guests. Tsar Nicholas I and Grand Duke Constantine stayed here. Currently, it is the seat of the Primary Music School. A rock situated in the park commemorates the builders of the Augustów Canal. It was placed there in 1973, on the 150th anniversary of the start of its construction.