The shared bathroom is actually two shower rooms in the garden by the pool; there are, though, two additional bathrooms in the wooden lodge where the guestrooms are located, each with a toilet and handbasin, so, once we got over our surprise, this was not a problem.
The location is great if you want to break the journey around the Golden Circle. The guesthouse is around 3 km off route 37, the road that goes from Thingvellir National Park to Geysir and Gullfoss and only about a 15-minute drive from the lake at Laugarvatn, where there is a very good restaurant, Lindin (booking recommended). The setting, in fields, is very peaceful. We enjoyed swimming in the small geothermal pool, soaking in the hot tub and drinking our breakfast coffee on the wooden deck. Excellent value at around 100 euros per night.