Backpack? Rear Pannier? Yes! Perfect for touring, commuting and biking/hiking adventures of all kinds, this do-it-all pack will carry your gear and keep it dry whether you're headed across campus, across town or across the country. The 18"x 12"x 3" main compartment is a removable 640 cubic inch dry bag. The outer 600 denier urethane coated nylon carrier has an 8"x 8" zippered top pocket, an 8"x12" zippered front panel pocket, a zippered 7"x10" front mesh sleeve, a mesh water bottle pocket and a zippered 6" side pocket. Four side compression straps and two vertical compression straps stabilize the load and provide an attachment point for a clip-on taillight. The interior of the pack features the main dry bag compartment, plus a 15"x 9" document sleeve and a zippered 11"x 5.5" pocket. In pannier mode, the bag attaches to any standard rear rack with hooks and a strap. When you transition from biking to hiking, simply zip off the pannier panel to reveal 2" wide contoured padded shoulder straps, an adjustable sternum strap, a removable waist strap and a padded rear panel. There's even space between the dry bag and the carrier to slip in a 70oz or 100oz hydration bladder.