Many mikva’ot – Hebrew for ritual baths, mikveh in the singular, – have been excavated in Jerusalem and elsewhere in Israel.
A mikveh usually takes the form of a stepped pool carved out of the rock with a small dividing wall built on the upper steps. The purpose of this was to allow users of the mikveh to descend on one side and, after immersion, ascend on the other side, thus preventing contact with those who were not yet purified. Most synagogues had ritual baths attached to them.
Washing and bathing are important parts of Jewish ritual and are referred to in the Gospels, e.g. Matthew 15.2 and John 9.7.