The small parking area before you climb Miðfell. This is where you go up (google maps directions make no sense) . The path leads over wooden steps, then up the mountain. Don't trust Google maps, trust geocaching!
Please note: there is another cache up on the mountains. However, the coordinates were wrong, so I disabled. If you want to try finding it, these are directions that worked for my intrepid FTFs: Go up to the mountain until you see the lake. You will see a path leading even further up the mountain. Go up there, and then to the left (the path circles the lake, a wonderful short and easy hike if you want). The cache is somewhere along the bank there to your left. Unfortunately, I can´t make it up there to fix the coordinates for a while. If you do find it, I would love to receive the correct coordinates so I can re-able the cache.