To call Seljalandsfoss an "adventure" in and of itself may be giving it a bit too much credit. Drive about 90 minutes (125 km) west from Reykjavik along the Ring Road, turn north on 249 just after you cross the bridge, and voila!, you're parked next to a bunch of other cars/buses, donning a waterproof jacket and following the telltale sound of camera shutters towards the misty falls about 100 meters directly in front of you. Snide remarks notwithstanding, however, you'd be doing yourself a real disservice by opting not to check out this incredibly beautiful cascade. Follow the footpath behind the roaring falls as the water plunges more than 60 meters onto the rocks below and you'll be treated to one of the most amazing views you'll find anywhere on Earth for such little effort.
Still not satisfied? Good, because there's another less crowded and more rugged waterfall nearby that can help to round out the adventurous side of this experience. Drive (or walk) another 700 meters north along 249 and you'll see a turnoff for Gljúfrafoss, or the Hidden Waterfall. Partially obscured by its own canyon, this picturesque cataract makes you work just a little to fully appreciate its beauty, which makes the experience all the more rewarding. Water levels permitting, trudge your way right in the canyon for some fantastic views at the base of the falls and enjoy the relative solitude.