The majority of Columbia's graduate and undergraduate studies are conducted in Morningside Heights on Seth Low's late-19th century vision of a university campus where all disciplines could be taught at one location. The campus was designed along Beaux-Arts planning principles by the architects McKim, Mead & White. Columbia's main campus occupies more than six city blocks, or , in Morningside Heights, New York City, a neighborhood that contains a number of academic institutions. The university owns over 7,800 apartments in Morningside Heights, housing faculty, graduate students, and staff. Almost two dozen undergraduate dormitories (purpose-built or converted) are located on campus or in Morningside Heights. Columbia University has an extensive tunnel system more than a century old, with the oldest portions predating the present campus. Some of these remain accessible to the public, while others have been cordoned off.