This was one of our favorite hot springs. We ended up on a tour of all the hot springs we could get to. We would pick a hot spring and make a day of getting to it from our rental house. I wish people would not leave their trash in at this spot, it was disappointing to see all the garbage left behind by probably visitors, who are ruining the thing that they are visiting because of its natural beauty.

First off, make sure to use the location in Google Maps to get here. Using other navigation apps. seemed to lead us elsewhere. Once there, we started off on the trail and it didn't start off so bad, but once we started to ascend the mountain, the 12" of snow, the wind, and light snowfall really starting to drain us. The hike itself isn't very long, but the snowy conditions added some extra difficulty.
About the hot spring... it's important to note that there wasn't any part of the spring that was particularly deep. I would say most of it was about a foot deep, with the deeper area being 2-3ft. deep. Though, it didn't stop us. The higher up you go, the hotter the water will be, so just climb up to your preferred temperature.

The only way back is the same way you came, so pack some snacks for a return journey. (this might not apply in summer)

We started this hike late in the afternoon and weren't too sure if we had left it too late but there were enough people on the hike that we passed that we were reassured. The café owner at the car park told us to allow 3 hours to get up and back and that was about right. The hike on the way up is steep in places but we only have a moderate level of fitness and we coped fine, walking poles might be handy if you struggle on inclines.
The hike wraps around the hillside and we got great views back over the area behind us. The further along you go you start to go past bubbling hot vents and the steam can fog your glasses. There is the smell that you get used to from the venting gases and at times you feel like you are in a whole different world with the ground hissing and steam coming out. There are areas that are roped so be careful as you pass them as they are there to keep you safe- watch where you walk and keep your eyes on the trail.
Once you arrive at the hot river there is a small changing area which is basically a wooden screen you can duck behind. The wind was whistling up the valley and so it felt colder than it actually was, plus you're warm after the hike so stripping down to your bathers feels chilly. We got in the river close to the changing area and it was lukewarm at best. We should have got out and gone further up the valley as it would have been warmer but the idea of getting out and getting cold as we ran further up was worse than the idea of sitting in a lukewarm river. Hint: head further up the river for warmer water.
The hike down was enjoyable, there were sheep, a distant waterfall and a fairly gentle descent. Folks were still coming up the mountain as we made our way down around 8pm, they had more confidence in the midnight sun still being up than we did.
Take lots of water. Use the toilets by the café. Watch your step while passing the venting steam. Enjoy a unique Icelandic experience!