I’m particularly amazed how you manage to find unusual objects in usual places, this time it was a nuclear bunkers that surprised me a lot!
The city is riddled with them, it's said there are about 500 in Tbilisi alone. I know the location of about two or three of them at this point. But yeah, even in the Botanical Garden, quite close to the entrance on the side of Mother Georgia, you'll see these huge metal doors that go into the mountain. They're nuclear blast doors. The most telling sign tends to be their ventilation shafts either near the doors or poking out of the ground in the surrounding area. Just casually sitting there in the garden! They're huge so you won't miss them if you're walking by the waterfall.
Tskaltubo
I haven't been there but it's definitely on my list for those buildings. A place I would love to visit just to fly the drone around and capture from above. Given those sanatoriums were often for the Soviet Union's more elite groups, I have no doubts that area is also coated in underground secrets.