I've been trying to bring rope into Ghost Town to see if there is an area under the elevator.
There isn't, but it was planned. It wasn't done before the end of 2238 (wasn't even started).
Basically there would be an alternative route to the facility through severs.
Also under the facility there was supposed to be entrance to Vault 17, originally the plan was
to put HQ chemicals there but I would rather keep them on the surface in similar fashion like
they are now in Waterworks (so only surface map would have to be done to add the HQ chems)
and leave the vault as a possible quest location for later: to retrieve scientific data from the Vault
for Dr Fung in San Francisco. You would have to come with your own holotape, go down, find the
computer with the data (maybe use energy cells to power the computer) and copy it on holotape.