Patal Bhuvaneshwar is a temple unique in its own glory! I haven't visited the temple, only watched about it in the Programme- 'Devbhumi Kumaon' on Doordarshan.
It is situated in Pitthoragarh district of Uttarakhand. The uniqueness lies in the fact that the temple is actually a cave, around 90 feet below the ground level, that is, we have to go down through many stairs to reach the mandir. And also, the road downwards has many ups and downs, that is, the temple has many floors. That is the reason it is called Patal Bhuvaneshwar. The narrow tunnel has forms of almost all Gods and Goddesses known to us. It is said to be the the abode of 33 koti Gods and Godesses.
It is situated in the meeting place of the three rivers- Ramganga, Sarayu and Gupt Ganga.
There is a story about Patal Bhuvaneshwar in Skanda Puran. This puran also refers to this place a sacred one, a must visit for the devotees.
The Govt website on Uttarakhand Tourism has a detailed description of the cave here:-
Visit to Patal Bhuvaneshwar
Do try to visit this unique abode of the divine :)
Om Namah Shivaya!