Floatation tanks
Spiritual 

[Created by John Lilly.  The best aid to meditation and relaxation, with great health benefits. The first manufacturer was Samadhi Tanks, in co-operation with John Lilly.  The first, and still the best book, on the subject was The Deep Self by John Lilly.]

Floatation Tank Association (FTA) Information about floatation, with FAQs, members' code of conduct and links to centres in the UK and Eire.
Tank centres UK

Lee and Glenn Perry Samadhi Tanks

With Timothy Leary