here are sites for local ( Calgary ) geocachers.
http://www.calgarycachers.ca/
http://members.shaw.ca/caching/pages/caches.htm ( which you can access from Emily's link as well )
It's actually an interest event to take your kids out for some treasure hunting and to have fun with the expensive toys, namely GPS or million dollar military equipment...like that comment..LOL.
Each item is given a location ( or called way point in the GPS world ) and hints or tips to help you locate the item. When you found the item, you can take it and put something else in or just leave it there for the next person.