We're spending a couple of days in a flat on Hazellville Rd N19 with our 19 month old DS. We aren't very familiar with London, and we're meeting some childless friends in the afternoons. Is there anywhere in walking distance we can go that would let DS burn off some energy, but would also be good for adults? I'm trying to think of rainy day plans, as the Heath or Waterlow Park will be great if it's dry. Thank you!