It's a plant called Salvia Divinorum. Read on erowid about it and the links Dutch Masta provided up top.

I can describe it as being much more intense than any acid I've taken. Luckily, it only lasts for a good 10min or so.

It is very intense, and I don't think size and body weight has anything to do with it. I'm 6'3, 220lbs, I'm a big guy, and 3 pipe rips of 10x fucks...me...up.

Sometimes you can buy it at your local headshop. Prices vary, but it is expensive. For a gram of 10x, I paid $30, and for a gram of 20x, it's $60. Prices maybe a little lower or higher.

Just don't buy the leaf. Buy the extract as smoking the leaf alone does nothing.

If you can't find it at a headshop, shop the interent, google it. You'll find tons of sites to buy it from.