Overall, we had a mixed time at the Guest Cottage.
Great parts: Walloon Lake is gorgeous! The shared dock, water access, beach, camp fire area are incredibly well put together. There is a small sandy area "beach" for young children to enjoy, with some rocks at the immediate shoreline. However, using the dock access, there is a completely sandy and superb swimming area starting about 10 feet out from the shoreline that extends a long ways before getting too deep. We had a blast swimming here as a family! I would give the beach, swimming and boating area 5/5! Note: There are stairs to get down to the beach, but our family aged 5-60 had no trouble.
The guest cottage itself can at times feel tight, but promotes you going outside, which is what you should do at such a beautiful spot. There is a spacious outdoor deck to eat meals and enjoy nature. The spiral staircase to the lower level has very secure locks for the little ones, which was great. The reviews of the beds in the upstairs was that they were functional, nothing great, but not bad.
Unfortunately, the disappointing part of the trip was for those of us who stayed in the walk out lower level. Our first night, the downstairs bed was so lumpy/rolly/mushy, my wife actually rolled off as we both went to lay down. For the rest of the trip, I slept on the trundle bed (best sized for a child, not grown man, lol) to try and give her more comfort (8mo pregnant at the time).
The other unfortunate part of the lower level, was the significant humidity and dampness. We did visit during hot, 85F humid days, but sheets felt wet when you went to lay on them, clothes too after 1 day, and everything developed a general damp/musty odor. A dehumidifier was running, but could not keep up. Certainly, the unseasonably warm weather played a role, but it is never to fun to settle into clammy sheets.
All told, my wife and I slept so miserably for the first few nights of the trip and despite the beauty of the location, we ended up leaving 2 days early due to sheer exhaustion.
Our strong recommendation would be to have a new bed placed in the downstairs bedroom if possible because this seriously detracted from what would have otherwise been a great vacation. A second dehumidifier may be helpful too. (I fully anticipate the owners will listen to this feedback, as they were great to work with for booking and clearly take a lot of pride in maintaining their beautiful property).