Things to know if from USA (or similar):
Use the address they give you in Google or Apple Maps and know that you are looking for unit 16. It is the THIRD floor, with no elevator. so if old, take it slow but I had no issue (45, healthiest, teo bags).
You cannot get in the INNER door until he gives you a key. Outer door is unlocked. Push the NO NAME on it, TOP button on the RIGHT when enter the foyer to call him so he can buzz you in. He will give you a key to get in the apartment inner door and his apartment once arrive.
He lives upstairs w his wife and your daughter. They are super quiet and interact as little or much as you want. I basically did the golden circle; southern coast; etc and just came back every night at 8 pm, shower, crash, repeat. They let you have access to their frig; stove; etc so if bring food like me (oatmeal, instant coffee, etc) they let me boil water; use utensils; etc. they do NOT have a microwave you Americans like me so don’t bring microwaveable foods. I didn’t ask to use their laundry machine but they seemed nice re such things (I brought my own Tide Deom America and washed clothes later in week at an apartment that had a washer and dryer).
It is 15 min + from downtown. Ie. Close if have car but ow you will need to taxi or find one of those w-scooters that are everywhere.
Bring bar soap if from USA. Every place in Iceland I found used the foam soap+hand approach. So bring bar of soap or use foam soap which they (and everyone) offer with a washcloth.
The showers IMO are all tepid. Every single hotel…. Geothermal to them _> warmish by American standards. I stayed at Fosshotel ($$$$) and it was also tepid. Just a heads up before you are surprised. The way to use Iceland showers is turn the RIGHT knob the farthest up or down (depending on what makes it hot… his has a child lock on it ther you push in to get it to the max heat). The LEFT handle controls volumed by mixing in the cold water. I always cranks the hot side to max and then turn the left one to volume I like.
Good luck. I did everything and Rick Steves book. As a whole I think Iceland is a 6 Max trip if have a car and fast. 1 days golden. 2 days southern loop. 1 day to just walk the capital and good meal (not much to do there IMO unless a foodie, young person that likes to drink?bar?etc, despite the adverts for the city; Pearl; iceland museum; Harpa; etc). I got bored of the city after a day and I walked everywhere w walking tour guide.