Below the Rosental Mitte site lies a tunnel system of around one kilometre in length. The hidden spaces are very important for the functioning of the entire site. The ELT (energy line tunnel) was largely built in the 1970s and 1980s and still forms the backbone of the technical infrastructure in Rosental today.

Numerous supply lines for energy, water, electricity and data run through the tunnel. The lines are designed as a ring network. This means that specific individual sections can be disconnected from the grid during maintenance or repair work, while supply to the remaining buildings is unaffected.

A major advantage of the ELT is that the lines are protected underground and do not have to be routed over visible pipe bridges. At the same time, leaks or damage can be quickly identified and easily repaired, as the pipes and cables can be accessed at all times.

Today, steam, hot water, drinking water and nitrogen are distributed through the tunnel, among other things. In addition, there are high- and medium-voltage lines, data connections, alarm cables and control cables. Whereas in the past around ten different ‘media’ were routed through the tunnel, today there are just four central pipes.

For security reasons, access is strictly regulated and only permitted upon registration. The tunnel has no direct external access points; it is only entered through designated access points inside the buildings. To increase safety, the structure is divided into several fire compartments. Static ventilation with additional extractor fans and drainage pits with sump pumps ensure reliable operation.

The most recent renovation concerned the lighting, which is now controlled by motion sensors. At the same time, the tunnel system is constantly being expanded: a new ELT section is currently under construction. There is also a connection to the civil engineering office (Tiefbauamt) tunnel, which runs under Badischer Bahnhof station into the Schoren district and is used to supply hot water.

Anyone who would like to explore the hidden underground world of Rosental Mitte for themselves has regular opportunities to do so: the free ‘Rosental Mitte Underground’ tour offers fascinating insights into the tunnel system and technical infrastructure. The dates are published on the Rosental Mitte website.