At first, I was worried that it had gone unnoticed for even longer than I thought and there might already be chicks in it. The nest looked completed, and we kept seeing the robin fly in with something small in its beak and then spending a while with its tail-feathers sticking up in the air. I thought it might be bringing food back to its chicks.
I had to use the ladder to check inside, and I was relieved to find it both empty and incomplete (the mud on the inside was still fresh). Although I did not like depriving the robin of the fruits of its labor, I also did not want to have a protective bird hanging around the entrance of our cabin and possibly attacking our guests. Thus, I removed the nest (and the remains of the first one). I'm glad we caught it soon enough.
However, I could almost swear I saw that bird give me a dirty look.