Taking a trip deep into the bowels of the WWII-era sub HMS Alliance is compelling, thanks to the lights, sounds and even smells used to create a sense that you're visiting just as the crew has gone ashore. HMS Alliance is in Gosport, across the harbour from Portsmouth; free water buses (30 minutes) shuttle to the site from Portsmouth Historic Dockyard.
The tour leads through the submarine's service years, from the 1940s to the 1970s, and sees you navigating cramped quarters and peering up through periscopes on to the harbour outside. Entry to the ship is included in the All Attractions combined ticket (adult/child/family £35/15/60).