Tariq Ahmad: Amazing park! Great for hiking and nice views. Gorge Trail is the most scenic and is 832 steps to the top. (Stairs are broken up into sets of 20-40 so it's more manageable.)
35 The Fenchurch Building, 20 Fenchurch St, London, Greater London
Scenic Lookout · City of London · 301 tips and reviews
Tariq Ahmad: Tickets go fast (although they are free). Be prepared to wait outside before entering the building, then going through security before going up.