rei no pool
Rei no pool (例のプール, lit. "the usual pool") is that indoor swimming pool with angled solarium windows which can be seen in just about every pool-related Japanese adult video ever.
It is located on the top floor of a building in Shinjuku, and was formerly part of a private penthouse apartment during the area's economic boom; it's now owned by a company that rents locations for video shoots. Surprisingly for a studio frequently used to film porn, it overlooks an elementary school.
Despite its reputation as a common location for JAVs, the pool has recently been featured in a handful of mainstream productions as well, including an episode of Kamen Rider Fourze.