The name of this temple, which is sometimes called Danjo Garan or Dai Garan, derives from the Sanskrit saṅghārāma, which means monastery. With eight principal buildings (temples, pagodas), the complex was the original centre for teaching established by Kōbō Daishi in the 9th century. It's still a teaching centre today, and you might see groups of saffron-robed novices making the rounds. The buildings have burned several times in the intermediate centuries and what you see today are almost entirely modern-day reconstructions.
Chūmon, the Garan's main gate, was renovated for Kōya-san's 1200th anniversary in 2015, after an 1843 fire. Two of the original statues of guardian kings enshrined in the gate were rescued from that fire, and two additional ones were carved to make the full set of four.
The most interesting structure in the grounds is the Konpon Daitō, a 50m-tall, bright-vermilion pagoda seated at what is considered to be the centre of the lotus-flower mandala formed by Kōya-san's eight mountains. The main object of worship is Dainichi-nyōrai (Cosmic Buddha), surrounded by four attendant Buddhas and, painted on pillars, 16 bodhisattvas, which together compose a three-dimensional mandala of the Shingon Buddhist cosmos.
The Kondō is the Garan's main hall and enshrines Yakushi Nyorai, the Buddha of medicine and healing; the actual statue is hidden, but there are mandalas and paintings of bodhisattvas and Buddhist teachings on the walls.