I like memory sports like memorizing decks of playing cards, Pi, mental calendar calculation, etc. It's done mostly offline but I use some online gadgets I made to enhance it. It's not physical but if you memorize while running (and collecting mnemonic 'journeys') or working out it's a nice combo. I count my exercise repetitions with the digits of Pi. Ron White trained while in scuba gear. http://www.mindtools.com/memory.html