The souterrain at Tungadale is one of the most interesting of the ancient sites on Skye. Getting to it involves a fairly long walk of around 16km for the return trip. Almost all of this is on a track that makes both the going and the navigation easy. The final short section is a little tricky though, and it is worth noting that the destination is a pretty remote spot.
I have in the past tried to reach this souterrain on a much shorter route from Amar, which is the only way I have seen documented elsewhere. Sadly, the bogs were completely impassable beyond the western end of Loch Duagrich. This longer, (but achievable) route leaves the Dunvegan - Sligachan road at NG390349 and runs via the Tungadale forest track over Bealach Mor. The track ends at NG409392. From there you need to follow a fire-break in the forest north towards the destination. To begin with this is easy, but the very last bit requires forcing your way downhill through dense forest. I'd seriously recommend marking your route on the ground at this point so that you can retrace your steps.
Then, unless you have a GPS, you may struggle to find the souterrain. To put it mildly, it is not in an obvious spot. The best I can say is that it is up a steep slope on your right hand side as you walk east along the north edge of the forest. It is about 200m from the end of the loch. If you have a GPS, set it to find NG4075440065 and you should be fine.
The Tungadale souterrain is part of a much bigger bronze age construction, consisting of what appear to be two virtually underground houses built of stone and terraced into the hillside. Its entrance is through a wall from the inside of one of these 'houses' and it runs a considerable distance underground. Even with a torch, and there being a bit of natural light coming in through a hole in the roof after three metres or so, an immunity from claustrophobia is useful if you want to be bold enough to crawl right to the end.