This is a nice, well-appointed house on the northern shore of Lake Arenal, near Aguacate and Nuevo Arenal. It is on the 142, a paved road, and in a small cluster with what look to be three other smaller buildings. It's well-situated to reach a couple of different landmarks, namely, about an hour's drive from Arenal itself (and thus the La Fortuna waterfall and a number of thermal springs), and an hour's drive from Tenorio/Rio Celeste. You're about 10-20 minutes away from towns with restaurants and stores.
The master bedroom has huge picture windows (and curtains for privacy) that look out on to the lake and the volcano in the distance. Since it was just the two of us staying there, we did not use the downstairs bedroom. There's a carport and driveway if you are renting a car. Everything was very clean when we arrived.
There is a handyman/assistant/concierge, Jose Luis, who lives in one of the other buildings nearby. I believe the owner, Elizabeth, also lives in one of those buildings. Both of them were very responsive to any concerns and a pleasure to deal with. Jose Luis was able to put us in touch with someone to arrange a private tour of one section of the Tenorio rainforest.
There is no air conditioner in the unit, and I don't believe there is a heater either. However, I didn't miss them. The temperature in this area in February was pretty moderate, and with the windows open there was a pleasant cross-breeze. There is a bit of wind noise when the wind picked up, even with windows closed. I would also note that the general Costa Rican practice of not using addresses is in full effect here, and we took a couple of passes to recognize where we were staying. If memory serves, there's a sign outside of the complex that says something like Casa Lago, which hopefully helps you find it.