She had to take off her mask so people could hear her!!!!!
A smaller version of this bunker may be underneath the circular garden next to Epstein's ranch house. This Kansas one has a visible ventilation area at the top, but Epstein could have a bunker that is connected to the adjacent house by a tunnel, and so the top would not need any openings at all in the garden.
In Kansas, there are lots of opportunities to build this kind of bunker above a cave system where water can drain away in the event of flooding.
These bunkers are often built in mountain areas to have a secret supply of water from a nearby watershed, and because of the elevation, and the commonly found sand and gravel soils in mountains, there is an opportunity for hidden drainage back into the watershed.
Not saying that everyone engineers these things right, but some people are taking care to do it the right way. Unfortunately, many of them are criminals who won't have an opportunity to use their bunkers.