In ancient texts, Varanasi (Benares, Kashi), Rameshwaram, Kanchipuram, Dwarka, Puri, and Haridwar have been mentioned as particularly holy sites, along with geographies where major rivers meet (sangam) or join the sea.
An alternate reason for Tirtha, for some Hindus, is to respect wishes or in memory of a beloved person after his or her death.