On a budget, weigh it — Up at The O2 climb isn't cheap for what it is.
£35–£40
The clip-in walk up the springy fabric is a real little adrenaline hit, and the summit view over Canary Wharf and the river — especially at sunset — is fantastic. The honest catch: it's weather-dependent, has age and fitness minimums, and you're paying climb prices for a view the cheaper Greenwich high points partly share.