ᐅ My Wastewater System in an Old Timber-Framed House

Hello,
I took over my grandfather’s old half-timbered house in 2014. In the 1980s, my father renovated and renewed many parts. He was a craftsman and did almost everything himself. Unfortunately, he is no longer here, so I hope for your answers.

When I took over the house, the bathroom had been altered. It’s a very small room, now equipped with a walk-in shower and a toilet on the right side, and a washbasin on the left side. In the middle of the right side, the washing machine used to be placed, which had a separate drain for potential flooding. See photo.

Now I took a closer look at this open drain. You just have to remove the grate to see into a pipe about 15 cm (6 inches) deep. The pipe has a closed bottom, and it looks like no water could flow away there. When the shower runs, you can see how the water from the shower flows into this pipe from the left, but I don’t see any outlet. The floor cover has a small crack, as far as I could tell.
I’m wondering where the shower water actually goes? Does anyone know these types of pipe systems?
I’m trying to attach a photo.