From Lonely Planet: Kathmandu owes its name to this ancient building. The squat, medieval-looking building is especially busy in the early morning hours when the valley’s vegetable sellers set up shop and porters sit awaiting customers. Piles of smoked fish, banana leaves and marigolds spill into the surrounding alleyways.
Although its history is uncertain, local tradition says the three-roofed building was constructed around the 12th century from the wood of a single sal tree. It first served as a community centre where visitors gathered before major ceremonies (a mandap is a 16-pillared pilgrim shelter), but later it was converted to a temple dedicated to Gorakhnath, a 13th-century ascetic who was subsequently linked to the royal family. A central wooden enclosure houses the image of the god, which is noteworthy since
Gorakhnath is usually represented only by his footprints. In the corners of the building are four images of Ganesh. Across the square is the Kabindrapur Temple (Dhansa Dega), an ornate 17th-century performance pavilion that houses the god of music.
From Wikipedia: Kasthamandap (Sanskrit: काष्ठमन्डप, Nepal Bhasa:मरु सत्तल Maru Sattal; literally “Wood-Covered Shelter”) is a three-storied temple situated at Maru, Kathmandu. It is one of the largest and most noted pagodas of Nepal. The pagoda enshrines a statue of Gorakhnath.
This temple is built in pagoda style design. It was built in the early sixteenth century by King Laxmi Narsingha Malla. The whole temple is built from just wood of a single tree, and covered with the shrine.It is belived that it was made by artist named biset. The name of capital city is named after this temple. Once a year a huge ceremony is performed in the temple. On that day people gather around the temple, and they stay up all night. The people share the legendary stories about the temple, and enjoy themselves with different varieties of foods. This temple is one of the major tourist attractions too. Everyone is allowed to visit inside the temple, but people are not allowed to take photographs inside the temple. The temple is open after mid day until midnight. The unique feature of Kasthamandap has made it the most noted pagoda of Nepal. The earthquake on 25th April 2015 caused severe damage to this temple.And destroy it.