I encourage caching by public transport. Take the Northern Line to Hampstead or Golders Green, walking distance from both stations should be just over 1km (uphill from Hampstead!). Alternatively, Bus 210 from Archway or Bus 268 from Finchley Road/Golders Green will take you within about about 300m of the cache. Also, on a bicycle you can get to less than 200m from the cache on roads.
Hampstead Heath
Hampstead Heath is North London's largest and probably most important green space. The wildest of London's parks has fields to run in, long grass to roll in, woods to hide in and, most famously, ponds to swim in. In north London this is THE place to get back to nature. Strewn with picnickers, cyclists, families and the rest, the heath is large enough and has enough copses, hills and mounds that a quiet spot is never far away.
Sandy Heath
Sandy Heath, also known as "the swamp", is an area at the northern end of the original Hampstead Heath (before the Extension was added). Large amounts of sand and gravel were excavated in this area for centuries for bricks and railway building. The largest amounts of sand were removed in the 1860s, when a part of the area along Spaniard's Road was sold to Midland Railway Co.
Today, the Sandy Heath is covered by a lot of ponds and swampy areas, and some steep hills and hollows left by centuries of sand-digging.
The Cache
You're looking for a classic "small" clip-lock box that will hold some small swaps and TBs. Cache is next to some water, at least if it has recently been raining. Some parts of the area can be very muddy and swampy! Stealth required as muggles can appear from most directions! Please take care to replace and cover the cache so that it can't easily be seen!
Take note of the letter and number under the lid for the bonus cache.
Wheelchair Users
Unfortunately, no good weelchair access in this area (bumpy and muddy)