What should I do to celebrate?

It's my 25th graduation anniversary from high school this year. Where did the time GO??? I graduated in 2000 and didn't even realize it was this year!! I got an invite to a party reunion for it but most of the people were really stand offish. I only had two friends. I won't be going but maybe I'll celebrate in some way myself. I rarely go out or do anything fun. What should I do?