Dettifoss definitely blew us away with its sheer size and power. Perhaps a waterfall so wild and fierce was befitting of an area that just screamed natural and raw as it flowed on the glacial river Jökulsá á Fjöllum ("YUK-ul-sou ow FYUHT-lum") meandering through Iceland's version of the Grand Canyon - Jökulsárgljúfur ("YUK-ul-sour-glyoo-fur"). And to back up our adjectives, we've learned that this falls was said to have a flow of about 500 cubic meters per second at high flow, with dimensions of 44m tall and 100m wide. Add it all up and we witnessed a monster that was quite possibly Europe's largest and most powerful waterfall (let alone Iceland's biggest). The milky color of the waterfall was due to the fact that the massive river was fed by the sediment-rich meltwaters of the vast Vatnajökull glacier.
Given the wild nature of the falls (it was unregulated and protected by being part of the vast Vatnajökull National Park [it was Jökulsárgljúfur National Park or Jökulsárgljúfur þjóðgarður when we were there in 2007]), its rate of erosion (and therefore its propensity to move further upstream) was very high. Such raw power and fury almost made it feel like the ground was trembling beneath our feet, which made us very hesitant to get too close to the edge and potentially fall into the raging and frigidly cold river (there were no guard rails)!
We managed to experience this waterfall from both sides of the river - each quite different in their own way. So we'll describe the experiences separately.
Directions: Because the Jökulsá á Fjöllum River could not be crossed in the vicinity of Dettifoss, there were two separate roads that left the Ring Road - one for each side of the river. The specific directions and descriptions are further below.
If you want to visit both sides of the river, your only opportunities to cross the river are where the Ring Road bridges the river to the south (it's about 19km between F862 and Route 864) and where Route 85 bridges the river near Ásbyrgí to the north (it's about 4km between the Route 864 and the Dettifossvegur on Route 862).
From the car park, we hiked a well-marked gently downhill trail through some rugged basaltic lava terrain. During the descent, we were able to look right into the rugged Jökulsárgljúfur canyon. When the trail veered back towards the waterfall, we had plenty of options to scramble towards the edge of the gorge to look at the waterfall from a variety of spots. That said, we definitely had to be careful as there were no guardrails to keep us away from the edge. Basically it was up to our discretion to get as close as we thought was safe, but I'd imagine this would be reason to keep a very close eye on kids who don't know any better or adults who feel the need to live dangerously.
I believe it took us on the order of 20-30 minutes walk to get from the official car park to the falls overlook area.
While on the east bank, we got angled and profile views of Dettifoss near its brink. The lookout area on this side was long so it was also possible to scramble a little further downstream to get better views of the entire falls including its misty and inaccessible base. The trail continued further upstream from the brink of the falls where there was a fairly straightforward walking path that went to the brink of the horseshoe-shaped Selfoss (see that page for more details).
The east bank required driving on a bumpy unsealed 2wd road on Route 864 (though this route was not nearly as rough as the route to the West Bank as even tour bases would take it). It was for this reason that it was far busier and more popular than the west side.
To access the east bank from Reykjalið, head east on the Ring Road for about 37km (or 19km beyond the turnoff for Route 862). Just beyond the bridge over Jökulsá á Fjöllum, turn left onto Route 864 and follow this wide and relatively tame unsealed road for about 31km. There's a signposted turnoff to the left leading the last kilometer to the car park.
Overall, the drive from Reykjalið to the east bank of the falls took us a little over an hour.
From the car park, we hiked a 10- or 15-minute trail that went through a stark moonscape of black terrain without a hint of the waterfall even being here. It wasn't until the trail briefly climbed towards a rocky bluff did the final descent to the river and the waterfall was finally revealed.
The trail ultimately descended right onto the cliff that was both obstructing views of the bottom of the falls from this side as well as getting us face-to-face with mammoth waterfall. There were some low rope barricades to suggest to us not to go any further. Also, some parts of the ground here were wet from any mist that happened to be wafted up above the cliff then blown in our direction.
While experiencing the falls on the west bank, we got some dramatic close-up views while watching Dettifoss dwarf people on either side of the river! In the afternoon on a sunny day, we also managed to see rainbows in the wafting mist rising from the base of this thundering waterfall. It seemed like this was the place to be at this time of day, and the photo you see above came from the west bank in the late afternoon under sunny skies.
But with the fickle weather, we also happened to be on this side during a frigidly cold and rainy day where it was very difficult to see anything. That might be something to consider if the weather's foul and you're flexible enough to defer a visit here until the weather improves.
There was also a short trail that took us slightly further upstream for get distant view of Selfoss.
To reach the west bank, drive east along the Ring Road from Reykjalið on the eastern shores of Mývatn for about 18km (in case you didn't know, Mývatn translated as "Midge Lake", yikes!). Then, turn left onto the rough and rugged signposted 4wd route 862 (though we've seen some 2wd risk damage to their rental car to get here). Continue about 20km from the Ring Road then turn right at the signposted turnoff for Dettifoss. Ignoring another turnoff for Hafragilsfoss at 1.8km from the turnoff, continue another 1.3km to the car park.
From looking at our logs, driving from Reykjalið to the west bank of Dettifoss also took us an hour.