With all the talk of water/steam pressure on this forum there must be some steam engine enthusiasts amongst you.
For a brilliant day out and if you're in/near the South East I can recommend a trip on the paddle steamer Waverley - especially the trip that sails through Tower Bridge. We did the trip last week from Dover, round the Kent coast to Tower Bridge - took about 7 hours - glorious weather - sea not too choppy - and the sail up the Thames was especially impressive - and because it's steam power there was no humming of engines - just the paddles and the steam - you can also see the engines working.
There are a few trips this month which sail from Tilbury through Tower Bridge (about 2 hours) or from Tower bridge. Some include coach return. Well worth it if you can manage it. Check out details here then click on the Thames link on the right of the page.
PS I have intentionally not mentioned the coffee ....