United Kingdom
The Bone Caves in Sutherland, Scotland.
Between Ullapool and Lochinver, just before arriving art Loch Assynt, is a signposted car park and walk to the Bone Caves, so called because the remains of now extinct bear, lynx wolf and arctic fox have been found there. A wonderful walk on a good path then a final scramble takes you back 7,000 years to one of the earliest signs of habitation in Scotland. In this primeval landscape it is easy to sit there and imagine how it must have been to live there. This is limestone country and on the way there you pass by springs welling up from under the ground and entrances to the passages they have carved through the rock. Here is the longest underground cave system in Scotland and over two kilometres have been explored so far but they are for experienced cavers only so stick to the ones above ground.
www.walkhighlands.co.uk/ullapool/bonecaves.shtml
Google map: bit.ly/qh0oEY