Hverir is a location in northern Iceland that I have also visited twice now. Originally we didn't plan to go there again but we had some spare time and the weather was good enough so we still decided to go.
This landscape has a reddish color and that's why it looks like Mars or something. The ground is acidic so there is no vegetation.
There are many boiling mud pots and a whole area smells like rotten eggs due to sulfur. In there you should only walk in a designated path because you don't want to step into a boiling ground.
There is also a short hiking path leading up in the mountain. I have been there 2 times but never had enough time to actually go up there. Hopefully third time I have lol.
On the ground, you can see many crystallized sulphur deposit patches. By the way, is it right to say sulfur or sulphur, I actually don't know and it seems like both are correct lol.
It's probably best to not spend more than an hour breathing in sulfur because it's a poisonous gas and you will get intoxicated at some point.
This environment is hostile but definitely a very spectacular site to go and visit.