In the 16th century some Roman Catholics were meeting in secret - they were supposed to be plotting the downfall of all the local protestants (yeah right). There's a really hyped up version on p89 of this* which involves them being found in this cave, and the priest being hanged drawn and quartered in a field below - not to mention his dried up disembodied hand kept at a nearby house.
But the Welsh National Biography site http://yba.llgc.org.uk/en/s-DAVI-WIL-1593.html
has a slightly less hysterical version, where they are living in the inaccessable cave for nearly a year, and escape, and are only caught years later (one of them indeed getting hanged in the end, unfortunately).
*of 'Notes of Family Excursions in North Wales', by J. O. Halliwell, 1860. To be fair he is quoting 'Williams' History of Aberconwy, 1835'. Online at Google Books.