There appears to be a major archaeological monument on Hampstead Heath - a Bronze Age barrow, or burial mound. It stands near the top of one of the meadows, on the false crest, and it has been planted with trees to make it a feature in the landscape.
Folklore calls it 'Boadicea's Grave', in the belief that Boadicea (Boudica) was buried here after she had been defeated by the Romans. However it looks like a typical Bronze Age round barrow, dating to 2,000 to 3,000 BC.
However there appears to be considerable doubt as to whether it is a Bronze Age barrow. It does not appear on a sixteenth century map, the first appearance being in a drawing by Stukeley, made in 1725.
Here
is a close-up of the barrow, with the vegetation now cleared off it, so
that it shows quite clearly the extent of the mound. 
Another
view of the barrow, this time taken in winter, when the vegetation has
died down. This shows its position more clearly, and the fence that surrounds
it. 
From the barrow there is a fine view down hill, towards the east end of
London and towards the mouth of the River Thames. The Beaker folk, who
are often buried in such barrows, came originally from the continent,
and one wonders whether the barrow was deliberately sited to give a view
towards the mouth of the Thames, from which their ancestors may have arrived.