The former Jökulsárgljúfur National Park is now part of the Vatnajökull National Park. This area is dominated by the river Jökulsá á Fjöllum, which runs from the Vatnajökull glacier.
The river canyon is impressive and counts some of the most exiting waterfalls of the world. There are many interesting sights here, and the best way to explore them is on foot. You can string shorter hikes together and make a multi-day walk along the canyon.