Yeah I live in the town. I went back up there today with my girlfriend. Unfortunately part of the tunnels are blocked off as the hallway above had collapsed in so I couldn't get to the mortuary. I didn't want to spend too much time down there since the place is littered with asbestos and I only had my phone for a torch.
From my memory its a pretty small room with a slab in the centre and a smaller room at the back which looked like body storage. Weirdly the ceiling of the room is lower than the tunnels leading to it. I'll be heading back up over the next few weeks to show some friends around so I'll see if I can find an entrance on the other side.
I spotted a Youtuber on a 'signature board' inside the building and found this video, fast forward to 4.20 to get an idea of what the tunnels look like.