Isambard Kingdom Brunel's original entrance to the world's first underwater tunnel is to be turned into a cultural venue for music performances, theatre and events.

The 65ft (19.8m) deep entrance shaft to the Thames Tunnel, in Rotherhithe, London, was the first project the famous engineer worked on. Architectural practice Tate Harmer has now designed a freestanding cantilevered staircase that will provide public access to the circular ‘sinking shaft’ for the first time in 150 years. The staircase will also come with a high level viewing platform.

There will be capacity for up to 135 people at the new venue, which will also be available for hire. Construction work is expected to be completed later this year.

The project was conceived by the Brunel Museum and will also include a redesigned public entrance. It is the first phase of a wider masterplan for the museum, developed in collaboration with Grimshaw Architects.

The Thames Tunnel, which connects Rotherhithe to Wapping, was originally intended to be used by horse-drawn carriages, with work beginning in 1825 led by Brunel’s father, Marc.

However, the project was beset by problems – such as flooding and financial difficulties – and was only completed in 1843, with the younger Brunel having taking control in 1826.

Nevertheless, the tunnel became a major tourist attraction, with two million pedestrians passing through each year. Later used by trains, the tunnel is considered the birthplace of the London Underground system, and now forms part of the London Overground railway network.