When I turned 30, I went to my family's cabin on the river with my family- mom, dad, bro (& his family), aunt, uncle, cousins (& and their families)- and about 10 close friends. We spent the weekend floating, drinking, playing cards, and just hanging out. It was great.
For a female friend we rented a cabin at the lake and just hung out drinking and reminiscing. We did rent a pontoon boat for a day and motored around the lake. A good time was had by all.
What ever you decide to do, make sure your loved ones are there to share it with. And remember
NO PHOTOGRAPHIC EVIDENCE!! It may come back to haunt you, trust me.