https://balkansinsite.pollsandpolitics.gr/the-mystery-of-tsarichina/
From 1990-1992, a series of covert operations and excavations took place in a village, named Tsarichina, 30 km northwest from the capital of Bulgaria - Sofia. These excavations marked the start of the biggest contemporary mystery in Bulgarian history – a simple mystification in search of sensationalism, a giant government cover-up with millions of money spent, or an expedition in search of extraterrestrial life and the answer to our origins – what exactly happened in Bulgaria's „Area 51“ remains unknown. .... Loginova claimed she can speak with extraterrestrial civilization and the extraterrestrial beings have shown her different location of the treasure, or the alleged „being“ ... Loginova consulted with the most prominent Bulgarian mystic of all-time, Baba Vanga. Contradictory statements claim that Vanga told not to open or look for what is inside. Loginova herself began to take notes with hieroglyphic-like characters, which she claimed were guidance from aliens – by further stating that the notes she was taking were about the „birth of the Earth“.

https://mysteriousuniverse.org/2020/11/high-strangeness-and-aliens-at-a-mysterious-hole-in-bulgaria/
The military apparently nevertheless went into that tunnel to try and excavate the object, and along the way they discovered other anomalies down there, such as a slab in the shape of a concave lens, a depiction in the stone of a humanoid figure of a height dwarfing that of a human, and another tunnel with completely smooth walls, a silvery floor, and walls covered in some sort of hieroglyphics. When they actually tried to approach the slab that they had come from, it was reported that they were repelled by a bright beam of light, and what seemed to be some kind of invisible force field that kept them from getting too close to it. The psychic Vanga warned that the cave was protected, and that whatever was down there was not yet ready to be discovered by humans, that it would defend itself with violent force, if necessary. ...the clairvoyant Gina Demirova would warn of this: When excavations in Tsarichina were held, the aliens told me that the research must stop. Do not dig, it’s not your time! There is the center of the Earth - at a depth of 2000 km, there is a finding such as crystals. It is big as the sun when it rises. Do not touch! People will not reach it, but they will disturb the atmosphere. This is a big crystal, which is dangerous and will stay there as long as the Earth. It controls its movement. Stop digging because the earth will perish. Hard days will come for your people. There will be new, many terrible diseases, if you dig in Tsarichina. In the hole, there is underworld, but this is not hell. There are live people like you down there, but their origin is different. There is also space device that is found there. It was sent by an extraterrestrial civilization. There are cosmonauts down there. Thousands of years ago, when your country did not exist, a civilization from another planet sent a spaceship with three astronauts on Earth. They were not humans but robots. They were sent to explore life on Earth. They suffered damage and the space-ship crashed in Tsarichina. With every meter of digging down there, higher and higher radiation will be emitted. Do not dig into Tsarichina hole, it is not your time now!

It almost sounds like an Ark is down there.
It has some very similar indicators like the hieroglyphics - the Crystal - the floors.
The Ark is said to have a portal.
This is really interesting!

https://dailyoccult.com/secret-military-excavation-at-the-mysterious-tsarichina-hole-and-baba-vangas-prediction-about-alien-technology-inside-it-3/
Despite the warning, military continued their excavations, and various anomalous phenomena began to occur in the Tsarichina region, which frightened the villagers deeply. They saw UFOs in the area, ghostly pictures, and some of them even claimed that they had thoughts that were not their own.
In total, these excavations lasted for two years and all this time, the psychic Loginova said that she was constantly in telepathic contact with those creatures that were sitting there deep in the tunnel. They transmitted various messages through her in the form of fancy codes and she deciphered them.

“These were encrypted letters, in total I received over a thousand pages of codes during the excavation of Tsarichina. The texts are incredible. This is a collection of ancient scriptures telling about the history of man’s creation. How he was created, how he was brought to Earth, how he should survive, and what we must do to keep the Earth alive... The earth is part of the overall planetary synchronicity. This cosmic civilization wants the Earth to survive. Synchronicity cannot be broken, because then the chaos will come. This information is contained in codes, in an encrypted letter received in Tsarichino... They also talk about the so-called energy people. They are marked by them, and through the energy of humans, they maintain synchronicity on Earth. They prefer to make contact in order to get this information, because it is very difficult, and not every brain can process this amount of information. I know this is true." -- Elisaveta Loginova

Other psychics were also involved in the excavation, but majority of them could not stand such a volume of work and quit. For some, telepathic messages acted like a shock and they simply could not stand it. For example, another psychic with a long-term vision, Marina Naplatanova, committed suicide during excavations.

On November 19, 1992, the military unexpectedly gathered all their people, tents, equipment, and then began pouring concrete into the Tsarichina hole to seal it forever. When they closed everything up tightly, they left and never came back here. No explanation was given as to why they abandoned the project, and indeed no official reason at all as to why they were there at all. All the alleged evidence that was gathered regarding what was found in the tunnels was destroyed or marked as classified and buried in secret archives.

“All notebooks (with codes and transcripts) mysteriously disappeared along with all the magazines that we compiled in Tsarichino. The film that we shot before the closure of the project also mysteriously disappeared. I have no evidence left to confirm our work. I can use only your words and hope that people will believe me." -- Elisaveta Loginova

I have a friend that is from and lives in Sofia, I've asked him to comment on this. Will post if he does.