Graduate shows 2016: the UK's high-speed railway network could incorporate an underground swimming pool, museum and concert hall, suggests Royal College of Art graduate Ciaran Scannell.

Scannell has designed a one-kilometre extension to the proposed HS2 railway network that aims to link London with Birmingham, Leeds, Sheffield and Manchester by 2033.

The project, entitled The 18th Mile of HS2, imagines a "fantastical world" of concrete-lined tunnels that host a series of cultural facilities alongside the transport network.

"In 2024, HS2 will drill 17 kilometres below the streets of London... It will now drill 18 kilometres," said Scannell.

"This new fraction will become a sequence of subterranean cultural spaces – cultural infrastructure – accommodating swimming pools, an archaeological museum and climaxing in a new home for the London Symphony Orchestra," he added.

Scannell developed the proposal for the masters programme in architecture at the Royal College of Art. He was part of the ADS2 study unit, led by tutors Asif Khan, Finn Williams and David Knight, which this year looked at sprawl.

Renderings show three separate spaces beneath Regent's Park Estate, a 1950s housing complex in the north of the city.

Spaces formed of intersecting cylindrical voids, created with a tunnel boring machine, create a concert venue for the London Symphony Orchestra, a public swimming pool and a vertically arranged archaeological museum.

Circular windows are shown tilted above ground level, flooding the foyer of the orchestral venue with light, while skylights in the barrel-vaulted ceiling illuminate the pool.

The plans offer a more optimistic future for the Regent's Park Estate, which is threatened with partial demolition by the construction of HS2 next year.

"Beyond a formal experimentation, the project is proposing an alternative way of thinking about the provision of cultural amenity in London to completely re-imagine the potential of the subterranean as a new frontier for the cities growth," said Scannell.

The 18th Mile of HS2 is on display as part of ShowRCA. Dezeen is media partner for the graduate exhibition, which runs from 26 June to 3 July.

Other highlights include a toaster that sneezes out bread crumbs and a vacuum cleaner that poos, a proposal to relocate the Parthenon from Athens to London and a design for a gridded megastructure.