We spent most of the day at the Marble Arch Caves today and thoroughly enjoyed ourselves. The exhibition area prior to entering the caves details the story of how they were formed and also how they were found and explored. The caves themselves had a fun boat ride and lots of rock formations, including some we had not seen in other caves.
One word of caution: The trip into the caves is a long way down, and at the end of the approximately 1hr 30min visit, there are 150 steps to climb back to civilisation. We didn’t see this in the literature or even at the ticket office, although it was explained at the beginning of the tour. It was no problem for us, but visitors need to be aware of this before booking.