I doubt that bath was the first indoor swimming pool ever built. Perhaps in England, but not in areas closer to Rome. I just finished reading the historical novel “Pompeii” by Robert Harris. The hero of the book is a water works engineer. It is an interesting book especially for those interested in catastrophes and ancient engineering. Heated bathing facilities were a well established feature in 79 AD, and must have taken a number of centuries to perfect.
I saw an interesting article in National Geographic from about 25 years ago. It was about the excavation of a 50 foot high settlement mound in Bulgaria. The lowest level also dated to some time around 5,000 BC, and the pottery was very cheerful and colorful. By 3,000 BC, although the pottery was well shaped it was monocrome, gray and depressing. I always wondered what had happened in the intervening period.
Perhaps this one?
Karanovo Settlement Mound
It is located close to the village of Karanovo, 40 km southwest of Sliven and 10 km west of Nova Zagpra.
This is the largest settlement mound in the territory of Europe. Seven consecutive archaeological cultural strata have been found in it, reflecting the stages of development of the material culture of the prehistoric society in Thrace. The strata prove that there had been settlements in the course of 4 millennia – from the 6th millennium B.C. (early New Stone Age) to the 2nd millennium B.C. (early Bronze Age). As a result of the investigations, the Karanovo chronological system has been worked out, serving as a standard in the synchronization of the European pre-historical cultures.
Some of the archaeological finds are in a specially built structure by the side of the mound
