But the chimneys must be very useful in keeping the ice for a long time.
There might be a secret in the chimneys in preserving the ice for a long time.

I tried checking on Google but didn't see the answer so definitely its an unresolved riddle but I learnt the floor was covered with limestone and it was slanted to allow the dissolved ice (water) leave the place read more here

If you find the answer I would like to know resteemed post so I can easily read more commentd.....nice post @slowwalker!!!