Hi, you can find a photo at following link: https://imgur.com/a/zhI8KF6
The best way to find the tunnel, is to follow Voetweg 109. You have to walk halfway up the grading of the railway, over the Herk, down the stairs.
I used Komoot to plan a running session, which led me here. On screen, I thought it was the old connection of the Molenveldstraat (long time ago it was linked next to the Paenhuisstraat 30). It was not :)