There are a number of caves in the area but the main cave of pilgrimage is the Maratika Treasury Cave. It is here that Guru Rinpoche, with his consort Mandarava, achieved immortal life through the practice of Amitayus.
The caves of Maratika are mentioned in Tibetan literature from the twelfth century onwards. A biography of Guru Rinpoche, discovered by Nyangrel Nyima Ozer, describes why the Maratika caves are a sacred place for Buddhists. Other written sources say that at the request of the Bodhisattva Avalokiteshvara, Buddha Amitabha taught the eighteen tantras of Long Life. The dakinis wrote them down in their symbolic script using melted lapis lazuli on golden paper, and deposited them in a box made of five precious jewels, which they concealed in the secret Maratika cave. There are said to be many treasures buried in this holy place
http://www.mandalamagazine.org/archives/mandala-issues-for-2008/june/the-caves-of-maratika/
Om soti. This supreme holy place is similar to Ogmin and Khachö buddha fields. The shape of this mountain resembles a heap of lotuses. Above, the lamas of the Eight Means of Attainment are arranged like a mass of clouds. In the middle dwells an assembly of rainbow-like deities. Below, the ocean of oath-bound protectors roars like thunder. In front, the offering goddesses perform their dance.
The first secret path on the right differentiates between virtue and sin and is the great path of the hot and cold hells. The stone path behind shows the narrow path of the intermediate state between death and rebirth. The path on the left is the great path purifying the defilements and obscurations of the womb and collecting the two accumulations of merit and wisdom. The rocky path in front is the great path purifying all sins and obscurations of immoral priests and monks who have broken their commitments. These four secret paths bring liberation from the eighteen hell realms
At that place there are self-created images of Brahma, Indra, Hayagriva and Dorje Phagmo in union, the naga king Taksaka (dGa’ bo ‘jog po), and a box of good fortune (g.yang gi gau) that grants the birth of sons and daughters and whatever one prays for. On the four directions are the four great kings; above are self-created umbrellas, victory banners, standards and canopies, and in the middle is a self-created prayer to the Guru written in the symbolic script of the dakinis. Inside the cave, above seven steps, is the self-created life vase used by Amitayus for bestowing the empowerment of immortality. There is no doubt that all the prayers addressed to it will be fulfilled. At the right of the life vase is the self-created body imprint of Amitayus visible on the rock.
The entrance of this place resembles a half moon and faces towards the east, while the path leading to it comes from the south. A large number of trees grow in that place, the birds sing melodiously and there are many sweetly scented flowers. In front is a self-created lake, and at the distance of an arrow shoot is the self-created, secret cave of the Guru.
The second entrance of this holy place is known as the meditation cave of the Eight Means of Attainment. Inside is the self-created stone of the flesh, blood and soul of liberating the female demons. At the left of this door is a white turquoise conch shell; just by hearing its sound, the evil states of cyclic existence are shattered. Five hundred arahats are said to have visited that place. Inside is the Guru’s blessed water. It is said that by putting that blessed water in the mouth, the five uninterrupted sins are purified. Also inside are the Guru’s footprint and the self-created, unobstructed door of the sky. Above are the Guru’s toilet and his self-created thighbone trumpet and hat. Because in that place their evil conduct becomes clear to them, sinful women and heretics avoid going there.
In front of the first entrance to that holy place is a lotus-like tree known as shimal in Nepali language. At the east is the peaceful assembly hall, at the south is the imprint of the Guru’s body and the assembly hall of hundred thousand dakinis, at the west is the meditation cave of Dorje Phagmo, and at the north is the self-created rock imprint of the Three Protectors. These are the signs related to pacifying, increasing, controlling and wrathful activities. At the southeast is the Manjushri Hill and at the southwest, the Vajrapani Hill.
When visiting that great place, the highest people will engage in longevity practices, the middle ones will perform offerings, and the lower ones will make prostrations and circumambulation. If one visits this great holy place called Halashe or Astonishing, one will not need to experience the lower realms.
http://www.maratika.org/history/history_maratika.html
Thus spoke the Great Guru.”