Hammat Tiberias, just south of the modern city, is the archaeological site that gives the hot springs their ancient pedigree. The remains include synagogues from the Roman and Byzantine periods, with the famous mosaic floor showing the zodiac, seasons, and a Torah shrine.
It is a compact site, but worth the detour if you like places where religious history feels lived-in rather than tidy. The nearby hot springs explain why settlement clustered here for so long.