We love taking a walk up Northala Hills (see on the map HERE) with Roland (as that's probably the only "exercise" we do together...well..ehm..let's leave it there :D) From the top, if it's a clear day, there are great views of the City. You can see all the "famous" buildings including The Shard, Gherkin, Telecom Tower and even the Millennium Wheel is just visible. The Fields have small fishing lakes (catch and release), large playground for kids which is seriously awesome (it's a must for all the parents, your kids will love it) and a cafe. Certainly worth a visit with plenty of parking but probably the best if avoided on weekends in the summer as it gets packed with large gatherings of people but I guess you will get that anywhere in London on a nice, warm, sunny day. The only negative thing probably is that the area only has one toilet (men/women) located where the cafe is, which is a disaster! I'm one of those who spends half of the day on the toilet so this means I'm not allowed to drink when we're out there as I'd be spending the entire day in the queue for the loo :D.