Complex sentence: There are numerous myths and legends associated with the caverns, the most well known of which is that during the Reformation local Catholics being persecuted by King Henry VIII took shelter in the caverns and conducted secret mass there.
Split into simpler sentences: There are numerous myths and legends associated with the caverns. The most famous is that, during the Reformation, local Catholics being persecuted by King Henry VIII took shelter in the caverns and conducted secret mass there.