i went on holiday to spain with my girlfriend and her parent and they layout of the place we stayed at is 2 rows of flats on the second floor of a building with balconies looking down on a pool, well me and my gf ha sex in this pool at 4 in the afternoon with kids at the other end (it was a big pool with a shallow and really really deep end so we were quite away from the kids) and my gf's parent sitting out on the balcony above us, i never found out whether they noticed what we were doing.