Built in the early 1980s, the Thames Barrier is the one of the largest and most high-tech flood defense systems in the world. The barrier, which is raised to protect the city during exceptionally high tides, has a starkly futuristic design—sometimes compared to a row of crashed UFOs, bobbing out of the river. Multimedia presentations, a film about the Thames's history, working models, and views of the barrier itself put the importance of the relationship between London and its river in perspective. It's a treat for science and engineering geeks, but probably too far out of the way if your interest is only casual.
1 Unity Way, Eastmoor St., London, SE18 5NJ, England