The granddaddy of all geocaching events. GeoWoodstock is an annual event where cachers all over the world take over a generally small area for a day. This year it's right here in Boonesboro, MD (about an hour and a half away). It's free to attend but there are also package deals if you'd like to enhance your event. If you plan on going, be sure to register (even for the free registrations). This has a chance of being a GIGA event but they need to know the number of registrations in advance.