Banteay Srey is unusual in more than one way. Firstly it is situated more than 30 kilometres north of the main concentration of temples. Secondly, it was built by a local dignitry rather than by a Khmer king. Also it has by far the best preserved carvings.
Banteay Srey literally means The Citadel of Women. It is small but the detail of the carvings make it a worthwhile detour and you can combine this with visits to Mount Kulen and the River of a Thousand Lingas nearby.