As I mentioned previously, day 3 of a 4-day Inca Trail trek is a scenery day. Leading off, not so far from the night 2 campsite, are the ruins of Runkurakay (about halfway up day 3’s climb to the next pass).
Runkurakay is a somewhat odd thing — unlike most Inca structures, it’s round with concentric walls. At least, that’s the story for the main building — there’s a smaller rectangular building downhill from it.
It’s thought that Runkurakay served as both a trail control point, and as a tambo (way station). So basically, an inn for travelers on the trail — but mostly for the chaskis (messengers) that were the life-blood of official communication in the Inca empire. Runners would carry a message as far as they could, as fast as they could (on foot), then hand it off to the next runner when they got to a tambo.
So the chaski system worked a lot like the U.S.’ old Pony Express — but without the ponies. Having merely hiked the Inca Trail, I have a lot of respect for anybody that could run it — especially for a living!