Perhaps now more famous amongst Heat-readers for the 'slebs who live in the surrounding streets of upmarket houses, the hill was once part of Henry VIII's hunting ground, and did not officially become designated as public open space until 1842.
There are great views into Central London and it's handy for Camden, St John's Wood and Chalk Farm...and the Zoo, so get climbing.
**********Update - 2pm**********
TFL's London Loop are also in Primrose Hill this lunchtime, with the following local suggestions:
1. Trojka Tea Restaurant & Room - A Ukranian and Polish restaurant.
2. Sardo Canale - Sardinian food by the canal.
3. The Engineer - A public house which attracts aforementioned 'slebs.
4. Marine Ices - A decent ice cream parlour.
Click here to see the location on a map.