Helsinki City Museum in Finland has announced an opening date of May 2016, following an €11m (US$12.3m, £8.4m) 18-month refurbishment of its premises, the most extensive transformation in the museum’s 105-year history.

Moving from its current home within Helsinki’s historical district to a new location in Senate Square, the museum will be made up of a group of five historical buildings surrounding three inner courtyards, opening up spaces never previously accessible to the public.

The development, which started in Q2 of 2014, includes 2,400sq m (25,800sq ft) of open public spaces and is part of a city-wide strategy to redevelop and rejuvenate Helsinki’s oldest areas.

The museum – which will be the only free-to-access major museum in Finland – has been completely reimagined. Taking into account the city’s constantly changing environment, the new Helsinki City Museum is focused around a new vision and public strategy, with public consultations every step of the way to allow public opinion to influence development.

The renovation of the museum buildings was designed by Arkkitehdit Davidsson Tarkela, with Hannele Storgårds and Aki Davidsson as the main architects, and Tuula Jeker as the project architect. The interior of the museum has been designed by Kakadu Oy. Design agency Werklig also contributed to the development.

The museum’s new home has been completely renovated with new spaces and routes opened up, and technology for modern exhibits installed. One 1960s building inside the block has been demolished and replaced by a new build, providing better access.

With its expansion the museum is incorporating the Children’s Town exhibition at Sederholm House. The museum is also working with the Hakasalmi Villa, the Burgher’s House, the Worker Housing Museum and the Tram Museum, which are are part of the City Museum's portfolio.

One of the museum’s key exhibits will be Time Machine, a space incorporating future tech to send visitors “back in time” to a realistic version of Helsinki in the past. Software company Futurice handled service design and the technological solutions as a partner in the project.

The museum’s opening programme, titled Helsinki Bites is designed to bring history to life with a walk back through time. The exhibition will showcase the museum’s collection of photographs and historical items, telling the story of Helsinki through resident’s personal stories. As part of the exhibition the museum has launched an open call in the city for the public to donate objects and stories that will paint a unique picture of relationships and histories from Helsinki.

“New museums have been rare to come across in Finland and free-to-enter museums even more so,” said Tiina Merisalo, Helsinki City Museum director. “We’re excited to welcome visitors into our new home, which was previously an unknown space to most people.”

Helsinki is currently undergoing a cultural transformation, spurred on by the €126m (£100m, US$160.5m) Guggenheim development. In addition to the landmark project, Helsinki is also redeveloping its central library to be completed in 2018, while the new-and-improved Helsinki City Museum will provide a platform for collective and individual activity that connects the past, present and future Helsinki.