Most old square-rigged ships had several "crows-nests" (if you are defining it as a railed-in platform on a mast. The highest was on the main royal mast (in other words, the highest of the 4 spars, joined end-to-end, that made up the main mast)- although these were only fitted to whalers. On HMS Rose, a replica of a Napoleonic frigate (which is 135 feet long on deck) the top of the main royal mast is 130 feet up.
As for crows nests:
On a sailing warship, there would be railed-in platforms at the maintop and maintopmast top (about 40 and 70 feet up). There are unrailed platforms higher up. Enclosed crow's-nests only appeared on Greenland whalers. These were about chest-high, with straw insulation, and had a rotating canvas shield to protect from the wind.