Hampstead Heath is famous for its expansive greene...

Hampstead Heath is famous for its expansive greenery, it's views from Parliament Hill and its swimming ponds.
I can't comment on the pools as we didn't take a dip, and the views from Parliament Hill are indeed worth the short climb, but the one thing that really made an impact on us was the size of the place. We got utterly, utterly lost here. Even armed with a vague online map we got completely turned around and ended up not even making it to Kenwood House or the animal enclosures as planned. This isn't a huge complaint as the scenery is so lush that it's pleasant simply walking around. However some signs or maps within the park would have made a HUGE difference to our experience.
Please note that the park, despite its size, is also very busy. Especially with dog walkers. We actually loved seeing all the different breeds but if you have allergies or don't like dogs this is not the place for you.
Finally, if you do one thing here make sure it's visiting the pergola. It's a beautiful piece of architecture with some stunning gardens in the surrounding area.