I believe we already have the technology to build bases inside mountains and the technology exists to pass through solid rock to get to these bases. That means there does not have to be 'holes' for the craft to access these inside mountain areas.
The reasoning is that we already have reports of craft going into water without slowing down and moving submerged at incredible speed. This means that they have the technology to alter the time-space in front of them and move through it.
These are the kind of questions that can get you banned.
They showed an example of this on that show about weird weather phenomenon. Turned out the erratic lights people were seeing were refracted light from headlights of cars on a road miles away.
Unrelated to the aircraft UFO sightings though.
Years ago there was a couple of JAL flights that sighted a UFO that has turned into something of a conspiracy theory.
I should add.. I believe most people now assume this was some kind of military flight that was seen.
If you read thru the UFO reports, many of the witnesses say the strange craft moved/ flew, in a strange way, almost like the air in front of it was getting out of its way.
'wobbling' is also something that is reported often, the UFO appears to wobble as it flies or hovers in one place.
Doesn't seem very impressive to me at all. The FAA can really only match specific aircraft to a radar return....and that requires they are already in the IFF system. An unknown target with no match and no ID is basically nothing but a blip on a screen.
In order to register as a blip though, the object must have physical mass, it must be something solid.