13 historic monuments, puzzles which are still not solved

4. Dolmen Caucasus, Russia

Scattered across the mountain slopes are charming small houses crafted from flat stones.

Each facade features a hole, securely sealed with a stopper. What's fascinating is that despite the plates weighing tons, they fit together so perfectly that not even a knife blade can slip between them. These artifacts date back an impressive five thousand years.

Some monuments, like the famous Volkonskaya, are known for their healing properties. Interestingly, the "dolmen tradition" can be found in various parts of the world.