The place is rammed full of old trains, buses and the like - plus a large raised area full of memorabilia ripped out of stations that have been refurbished.
There are usually a few extras laid on, such as the usual "train geek" stalls and a miniature railway, plus rides on a heritage bus.
If going, a couple of tips:
Buy tickets in advance - they last all weekend, and avoid the often lengthy queues on the door.
If taking a bag, make it a very small one as larger bags have to be left in the cloakroom. My camera bag just happens to snugly fit in their airport style measuring box - so I don't have to queue up to get my bag back when leaving.
Adults £10; Senior Citizens £8; Concessions/ Friends £6; Accompanied children under 16 / TfL staff free. Book in advance on 020 7565 7298 (or in person at the Covent Garden museum).