The SL Relay for Life is in its third year, and this weekend is the culmination of months of work and promotion.
Spread across four sims, the course has some great sights, music on tap and a bunch of entertainment and commemorative events scheduled (SL Insider has the full schedule listed). There are different themed areas such as Pinocchio and Tomb Raider to walk through in addition to chatting with other participants.
Like the Australian Relay For Life, groups have set up camping areas and the whole thing has that similar community spirit. You can even enjoy the sight of yor hair disappearing as you cross sims on the walk.
Do yourself a favour and do at least one virtual lap and donate some money for cancer support and research. Check it out in-world.