One of my absolute favorite hikes in Iceland. If you're looking to do this with a knowledgable and personal local guides, this is the experience you are looking for.
The Fimmvorduhals hike is a challenging but highly rewarding hike. You will pass through seemingly endless waterfalls (I counted 23 but others say more!), go through desolated volcanic landscape, have a chance to see the volcanic mountain tops which erupted few years ago (Pro tip: Dig a little into the ground on top, it is still warm), and encounter the magnificent overlook of surrounding glaciers and mountains. In short, this is a hike you will remember for a lifetime.
My colleague and friend Nina wrote a great piece on how to hike the [Fimmvorduhals mountain pass in one day](https://travelade.com/iceland/stories/how-hike-fimmvorduhals-mountain- pass-just-one-day/) and took great photos. Remember, do not attempt this hike on your own unless you are an experienced hiker, have looked at the weather forecast, and have the right gear and navigation equipments (gps, compass, maps).
If you are however looking for the best guides to do this hike with, this tour by Midgard adventures is great choice - they are local mountaineering and adventure guides from the surrounding area and offer a very personalized service which you can't go wrong with.