This waterfall has only become popular in the last few years when it was discovered. It is difficult to get to as the tide makes it accessible only for a short period of time.
@Tel Thank you for your comments. If you Google 'Secret Waterfall Donegal' you will get a site that you a full description on how to find it. But there is a risk in going to it if you don't take note of the Tide Tables. It is quite close to the town of Killybegs. Don't go on your own.