I remember when I visited the [Touro Synagogue](https://en.m.wikipedia.org/wiki/Touro_Synagogue) years ago I vaguely recall hearing about a secret door under the bimah. I don't remember seeing it ,but upon further investigation I found a picture online. However, the reason behind having such a trap door remains somewhat of a mystery. Does anyone have an authoritative account that explains why a synagogue would have such a trap door right beneath the bimah. 

Picture I found :

[![enter image description here](https://i.stack.imgur.com/dmjop.jpg)](https://i.stack.imgur.com/dmjop.jpg)

(forgive me if this is off-topic,I am not sure what category this question falls into,I guess it also depends what the purpose of the trap door was for)