昌平童夢館 at Akihabara, Tokyo

Chiyoda-ku public complex with a pool, library, school and sports facilities near Akihabara.

Shohei Domukan is a Chiyoda-ku public community complex in Sotokanda 3-chome, a five-minute walk from Suehirocho Station and seven minutes from Akihabara Station's Electric Town west exit.

Opened in 1996, the multi-use building houses Shohei Elementary School, a kindergarten, nursery, children's hall, a street-corner library, gymnasium and a fifth-floor heated indoor pool open to the public on weekday evenings and weekends. The rooftop playground and multipurpose rooms are available to residents when not in school use, with pool sessions around 600 yen for two hours.

If you want an affordable public swim or a quiet library stop near Akihabara, this community complex is a handy local facility.
Official: https://www.city.chiyoda.lg.jp/shisetsu/bunka/shoheidomu.html