The next time you're travelling to Greenwich, give the tube a miss and try the Docklands Light Railway instead.
These aren't your normal kind of trains. For starters, they don't have any cabins at the front, so you can sit directly behind the front window and see where you're going -- it's a bit like sitting on the top-deck of a double-decker bus.
Part of the route is on a normal train track, but a fair amount takes place on an elevated monorail, giving you a great view of the scenery as it whizzes past. The best bit is when it goes below ground (when it's descending under the Thames towards Cutty Sark station, of when it's approaching Bank station), because then you can see the tunnel twisting and turning ahead of you! It's almost like a roller-coaster ride.
You can ride it in exactly the same way you ride the London Underground (it's basically just another underground line), using an Oyster card, Visitor Oyster card, contactless card or travelcard. You can buy a Visitor Oyster card online if you like. You can also combine them with a London Pass, saving you even more money. You can get a travelcard from the TFL website.
There are plenty of routes to choose from, but Craig recommends catching it at Bank (the start of the line) and getting off at Canary Wharf (you will need to board the train that's heading towards Lewisham). The steel and glass skyscrapers at Canary Wharf are definitely worth a wander around. Have a read of Craig's Canary Wharf review to see what it's like.
You should definitely have a read of Craig's DLR review before you go. You might also enjoy his review of the London Underground. He's also put together a marathon journey around London as well, which combines a ride on the buses, boats, trains and DLR.
If you like events at Docklands Light Railway (DLR), then you might also like these other London events…
Hire a Boris Bike… and cycle around London – Every day
View from The Shard — London’s tallest building – Every day
Guided tour of Shakespeare’s Globe Theatre – Every day
Drop-in Drawing at the National Portrait Gallery – Every Friday