We hung out in Cusco for four days to give ourselves time to acclimatize to the altitude before doing the Inca Trail. At the time, I thought this was a little overkill but we decided it had to be done – as opposed to risking having one of our children come down with altitude sickness while on the trail. To further prepare, we took plenty of walks in the city and up the steep trail to Sacsayhuman – from where we took this photo of the city.
I recently spent a weekend in Keystone, Colorado (courtesy, generously, of Keystone Resort) and had my first personal experience of altitude sickness. It was like having morning sickness and a bad hangover at the same time. I was miserable. To avoid this if you are planning to go into the mountains any time soon, check out this great article on how to avoid altitude sickness when traveling in the mountains.
We did come down with altitude sickness (by flying to Puno first, which is 400m higher, which I would NOT rcommend) and having had it, I think four days was the minimum time I would want to wait to give yourself time to get over it before doing the Inca trail. We had six nights all up, which was definitely enough time, but we wouldn’t have been ready to walk after three nights. We were pretty much better by then, but one of our kids hadn’t really eaten for two days.