While not exactly /relaxing/ I always found sport and light competition to be a wonderful destressor. Something about pushing yourself, only really having to think about the moment, moving around physically active, it's just been good for me.
Also, bath:
Fill a bath with very hot water.
Use a space heater/light a fire/light a bunch of candles to make the bathroom itself really hot or at least hold the heat from the tub.
Salts in the tub.
Get a big bucket of ice water, a soup spoon, and a facecloth or two.
Put on some slow, relaxing music - not something you'd ever really want to listen to, just some light background noise. White noise isn't that much worse if you're okay with it, just want to block out the outside sounds.
Bring a large cup of prepared tea.
A pillow for your head doesn't hurt, especially if you have a water proof one.
Turn off bathroom lights (if you have candles, light one even if you're going the space heater route), lay in tub, occassionally putting the cold facecloth on your forehead, chest, or the back of your neck. Every couple minutes, run some cold water down your head with the spoon. Sip tea occasionally.
Don't think about anything - that's the hardest part. Just focus on the hot, and the cold, and the difference between them. Focus on your breathing. Close your eyes, and let yourself drift away. The splashes of cold water should help keep you awake, and insure the bath is restful and invigorating rather than leaving you groggy.