London Cable Car is a real time commitment — fit it in only if it's a priority.
Allow 30 min.
It's a fun, cheap five-minute float over the river with surprisingly good views of Canary Wharf and the O2. The honest catch: it links two not-very-touristy spots, the ride is over fast, and it's pure novelty rather than a destination — easy to feel it wasn't worth the detour unless you fold it into a Greenwich or O2 plan.