A porthole along (not through) the wall

Some nice people from Harvard invited me to come over to see if there was any interesting stone work on their property along Rt 2. I saw three things and am afraid I did not do a decent job calling attention to them. For example there was a stone wall made of ledge rock and running along the crest of an outcrop. Someone had built a little porthole perpendicular to the wall and it looked like the wall had been borrowed from to get the stones used in the porthole.
Here was another very minor but pretty feature right up near Rt 2. I suppose this is a spirit door.
The third thing was a rock-on-rock. Simple and elegant. The upper rock looks red and burnt.
These folks do not have a lot on their property but it looks like a little of each of the basic types of feature.