A 727-metre-long tunnel called the Nirmer Tunnel (Nirm Tunnel) was built between Stolberg and the location of modern Eilendorf at line-km 63.6 during the construction of the line and completed in 1841.
Both miners from Eschweiler and workers from the Leipzig–Dresden railway were employed in the construction of the tunnel, using a method known as core construction (Kernbauweise—using three narrow tunnels to build the walls of the final tunnel before the tunnel core was removed).
There were eight chimneys above the tunnel for the extraction of smoke produced by the steam locomotives.
During the Second World War a bunker was built over the west portal.
In 1963, it became clear that the cross-section of the tunnel, like the Königsdorf Tunnel and the Ichenberg Tunnel, was too narrow to allow the catenary to be installed.
Therefore, the Nirm tunnel was partially opened out and converted into two smaller tunnels lined with concrete.
The western tunnel is the Eilendorf Tunnel with a length of 357 metres (line-km 63.9) and the eastern tunnel is the Nirm Tunnel with a length of 125 metres.
Although the two newly constructed tunnels were designed for speeds of up to 200 km/h and high-speed tests had been carried out with class E 03 locomotives, the permissible top speed today is 130 km/h.

From 1944 to 1986, the Nirm block post was located at line-km 63.2.
A 727-metre-long tunnel called the Nirmer Tunnel (Nirm Tunnel) was built between Stolberg and the location of modern Eilendorf at line-km 63.6 during the construction of the line and completed in 1841. Both miners from Eschweiler and workers from the Leipzig–Dresden railway were employed in the construction of the tunnel, using a method known as core construction (Kernbauweise—using three narrow tunnels to build the walls of the final tunnel before the tunnel core was removed). There were eight chimneys above the tunnel for the extraction of smoke produced by the steam locomotives. During the Second World War a bunker was built over the west portal. In 1963, it became clear that the cross-section of the tunnel, like the Königsdorf Tunnel and the Ichenberg Tunnel, was too narrow to allow the catenary to be installed. Therefore, the Nirm tunnel was partially opened out and converted into two smaller tunnels lined with concrete. The western tunnel is the Eilendorf Tunnel with a length of 357 metres (line-km 63.9) and the eastern tunnel is the Nirm Tunnel with a length of 125 metres. Although the two newly constructed tunnels were designed for speeds of up to 200 km/h and high-speed tests had been carried out with class E 03 locomotives, the permissible top speed today is 130 km/h.
From 1944 to 1986, the Nirm block post was located at line-km 63.2.
Cologne–Aachen high-speed railway