This may not be much of a secret but deserves a mention. I find it hard to go anywhere near this place without having to go there. Freshly baked Beigels hot salt beef and it never closes, 24 hours a day 7 days a week.
This uninspiring sounding place is a disused railway line that runs along the roofline from Finsbury Park to Highgate. A great place to excerise and escape.