Punarjani Guha
From Infogalactic: the planetary knowledge core
Punarjani Guha is a 150-metre natural tunnel in a rocky cliff situated in Thiruvilwamala in Thrissur District of Kerala state.[1]
Ritual
The ritual can be practised only on Ekadasi and that also on the eleventh day of every lunar fortnight. The days is called Guruvayur Ekadasi or Vrischika Ekadasi day, in the Malayalam month of Vrishchikam. First the devotees has to take bath in the Papanasini Theertham, a water source near the cliff. It is believed that performing noozhal or crawling through the tunnel from one end to the other will wash away all of one’s sins and thus allow one to attain freedom from rebirth or Moksha. Only men are allowed to do the noozhal; women can't only visit the cave.[2][3][4]