Well not exactly in a cave and not exactly on Mendip but these are some of the longest straw formations in the UK. They are said to be up to 20 - 30ft long and are formed by water percolating through the lime mortar inside the vaulted West abutment of Bristol suspension bridge. Although long suspected as being hollow the vaults were not discovered until 2002 by a workman laying slabs on the abutment. Looking closely you will see that the West tower of the bridge is different in shape to the other one built on a solid base. This is because Brunel did not wish the tower corners to sit on top of the vault centres. The vaults lie on two levels within the abutment and the public tour takes one into two of the largest. You have to book online and usually there is a long waiting list.

For public access the abutment wall was drilled and a whole plug removed and stored to be replaced again if required.



The first vault showing original access hole in the roof.



The second vault on the tour accessible through a short tunnel.





Some of the stalagmites.

Suspension Bridge Hard Hat Tour.

https://www.cliftonbridge.org.uk/event/hard-hat-tour-leigh-woods-abutment

Not sure how you can spend a two hour tour in a cellar.  Perhaps OR will provide a trip report?

That's wonderful.

Even I could manage that.
Must book a trip.
Thanks OR 

Half the " tour " is a walk along the bridge learning about it's history and construction. To be honest my other hobby of antique bottle collecting drew me there. Must be stuffed with relics left behind by the builders. ( Try looking under your bath ). Nope. Not a thing.

Almost completely sold out for this year!

Must be competing with Gough's Cave Chris. The bridge vault tour is not cheap at around ?15. Yes. Very busy the folk on my tour booked before Christmas. You do get plenty of time though and they allow photos. Anyone going is advised to sort out parking as it's a nightmare in Clifton. Best place is up by the Leigh Woods car park but it's a long walk down.

I've retired from Cheddar Caves. The place is doomed.

I wonder how much longer the stals need to be before there is no mortar left holding the bridge up and it call comes crashing down into the Avon Gorge.

Chris.

ChrisJC said:

I wonder how much longer the stals need to be before there is no mortar left holding the bridge up and it call comes crashing down into the Avon Gorge.

Chris.

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if they reach the floor and become pillars they will hold the whole thing up 
mind you  you won't be able to walk through them, unless your a skinny git