Above-ground ruins Bronsdalgroeve 2019

The flyer published by VVV (tourist office) of Valkenburg for the 75th anniversary of the liberation in 2019 states: From the summer of 1944 a factory of the Philips Valvo Werke from Aachen was established in the Heidegroeve. There 900 (forced) workers worked on the production of radio receiving and transmitting equipment for the experimental (Junkers) JU-388 aircraft. …
From the spring of 1944 the Germans started making the underground Bronsdal limestone quarry suitable for housing a war factory, where about 250 BMW 801 aircraft engines had to be overhauled each month.
That seems more plausible because Aachen is closer than Eindhoven. The Heidegroeve is a few kilometers away, on the Plenkertstraat in Valkenburg.

Go to Streetview to see what is still remaining above ground of the production plant in front of the Bronsdal cave