Out in the modern entertainment district of Odaiba you'll find Tokyo's largest artificial hot spring complex. Oedo-Onsen-Monogatari is an Edo-era onsen theme park.
What the spa lacks in authenticity if makes up for in scope: there are six different types of baths with different temperatures and textures including a lukewarm “Summer Bath,” foot baths and even a special bath for dogs (the Tsunayoshi Bath Tub)! The water is drawn from 1400 meters below ground and is rich in sodium and chlorine ions that refresh and relieve muscle pains. All of the baths are separated by gender.
When you grow tired of soaking you can spend hours exploring the park and it's many places to drink and dine, shop and have your fortune told. The complex is open 24 hours and there is a hotel on site.
Opens 11:00 am – 9:00 am (next day), seven days a week. Last entry is at 7 am. Adult over age 12, ¥2,480 each（Sat & Sun ¥2,680, Special Day ¥2,880). Children age 4-12, ¥1,000 each. No fee for a child under age 4. Evening discount admission is ¥1,980 (Sat & Sun ¥2,180, Special Day ¥2,380). No child discount available, entry after 18:00. Late night premium is ¥2,000 after 2:00 am. Fees includes bath fee, Yukata robe fee, towel fee and facility usage fee.