With the exception of Uffington, I'm not that fond of White Horses (some of the newer ones are really 'orrible but then they're not ancient). What else... hill forts are pretty worn down and not really intrusive. The pyramids definitely spoil the view of Cairo - can't even see the city from some places ;-) What about Roman aqueducts and Chinese walls? Ancient constructions tend to blend in somehow but I can't quite put my finger on why - maybe it's because they're more often made of local material and not concrete and steel. Cotswold villages almost seem to have grown out of the land - in a way I suppose you could say they have.