And if you're looking for a nice little workout, try a "brick". It's essentially a bike workout followed immediately by a running workout. Most people will do 3-5 miles on a bike and 1-2 miles on a run for starters (repeating as able). Though no real bricks are involved [yet], I decided to head out Easter Sunday carrying all this shit on my back. Did about 17 miles on the bike, hopped off and ran 8 miles.
Total time was about 2hrs and 30mins, but the workout felt much longer. While it didn't quite match up to the 50 mile race I completed a month ago, it was a much faster pace, and a much harder (read: concrete) path to travel. With the weight, my knees were really feeling it. Fortunately, I was able to get right into a cold bath immediately following my workout to try and eliminate most of the aches I'd feel today.