Burgholztunnel

For reasons of environmental protection, tunneling was preferred to an above-ground variant and runs below the state forest Burgholz, which due to its rare trees should not be cut by road construction. Due to the steep gradient in the tunnel structure and the fact that only three meters of earth lay above the tunnel, the construction of the tunnel was technically demanding. With a complex emergency call and monitoring system and six cross-connections at a distance of around 266 meters between the tubes and emergency call cabins at a distance of around 133 meters, the tunnel fulfills high safety requirements.
de.wikipedia.org/wiki/Burgholztunnel

In the course of the new construction of the L418, a southern bypass of the city of Wuppertal, the Burgholz tunnel was opened to traffic on March 29, 2006.The tunnel with two tunnel tubes is the core of the construction work and with a length of 1.8 km it is the longest tunnel in North Rhine-Westphalia.Each tunnel tube has two lanes, each 3.50 m wide, and a hard shoulder. The route overcomes a height difference of 80 meters.
3,600 blasts were necessary to create the tunnel, 300,000 cubic meters of earth and rock had to be removed.The tunnel complies with the latest safety standards, with 6 cross connections between the tunnel tubes, two of which are passable, which can serve as possible escape routes.In addition, the tunnel was equipped with traffic control systems, electronically controlled ventilation systems, fire alarm systems, video surveillance, tunnel radio and orientation lighting. 84 video cameras and 26 measuring systems for fog and smoke alone ensure safety.With the tunnel construction, the section of the L418 cost a total of 81 million euros, which, for the first time, was privately financed. Construction and financing costs are initially processed via the capital market and the Landes repayments, starting from 2007, are distributed over 15 constant annual installments.Source: baukunst-nrw.de/objekte/Tunnel-Burgholz--425.htm

A wonderful hiking area in the middle of two big cities - so diverse that I sometimes ask myself why one actually goes on vacation to go hiking

The Kiesberg Tunnel is a road tunnel in the city of Wuppertal. The tunnel crosses the 282 meter high Kiesberg.
de.m.wikipedia.org/wiki/Kiesbergtunnel

Tunnel of the expressway on the Wupper between Wuppertal and the interesting Solingen district of Schloss Burg

de.wikipedia.org/wiki/Burgholztunnel