Swoyambhunath, the Monkey Temple, sits on its hill west of the old city. It is the oldest and most sacred of the valley's Buddhist sites, and the walk up its 400-plus steps is one of the things almost every visitor to Kathmandu ends up doing.
Fewer visitors know that for people who couldn't make the climb, the old city built a replica. Kathesimbu, tucked into the lanes just south of Thamel, was constructed so that the sick, the elderly, and the otherwise unable to make the pilgrimage to Swoyambhu could still gain the same merit without leaving the city. It was modelled directly on the hilltop stupa, with the same proportions, the same symbolic carvings, and the same arrangement of smaller stupas around the base.
That is why Kathesimbu is sometimes called the "little Swoyambhu." It isn't a copy for tourists. It is a working substitute, built for the people of the old city, and it has been quietly serving that role for centuries while Kathmandu grew up around it.