Another explanation; It could be 18th C parkland of Hunstrete House. If you look at an actual paper map and not a magical map, Hunstrete house, is a hotel, with what looks like an artificial lake in front of it, and the mound or tump is on the other side of the lake. This could be for a folly or pretend classical temple to sit on (bit like Stourhead)..
Following this through.. HUNstrete House has HAWHAW (old traitor in the last war) 20thC play on words?