It's quite close the the road, in the grounds of the restaurant de la Mont de Cordes (which has a very nice looking menu) where we asked for directions.
It was just 30 ms away from the eatery, cut into the top of small rocky rise. Bounias was even bigger than Castelets! The portal was arched at the same angle as the interior walls. The interior height is about 9 feet tall – imagine that 9 feet deep and rock cut! – and I paced it back for 14 long strides. An astonishing place! So HUGE and so hidden! There are no signs to it at all.