Primrose Hill is one of my favorite spots in London to hang out and just take in the skyline...and it's free! From the top of Primrose Hill, you can see popular views such as The Shard, Gherkin, St. Pauls Cathedral, The London Eye, and if you squint, Big Ben and the Houses of Parliament.
I recommend bring some food and a blanket and watch the sunset on top of the hill...it's truly breathtaking. Also, if you are a dog person like me, be prepared to see lots of pups roaming around! Some may even come up to you for a lil pat.