For those interested in architecture, or anyone who is just nosy, I can't recommend the London Open House weekend enough.
Climbing the Church Tower of St Mary's Hornsey High St reqrds you with an excellent view of the area plus interesting history.
This year there is an Art Deco walk in Wood Green (meet 10am outside Turnpike Lane station), a self guided tour of the Tower Gardens Estate as well as tours of the Odeon Muswell Hill and Bruce Castle. Lots of interesting stuff further afield, but don't try going up the Gherkin unless you like queuing!