I'm going to have 3 months and $4000 to do whatever I want. Ideas?

I'm starting grad school in September and rather than find an internship for the summer, I've decided to take the time off and do whatever I want. I realize how rare a 3-month period with next to no responsibilities is, so I'm jumping on the opportunity. I've got about $4000 that is completely expendable. I have other money saved away for emergency funds etc, so I'm not looking to play it safe and save the cash.

I'm hoping to make it as memorable/exciting/action-packed/etc as possible. So what're your ideas? What would you guys do? If it's important, I'm a male in his early 20s.