I see DVCR’s pictures are now gone from this thread
Thought I’d investigate the rumour of a tunnel leading down from GRI towards High Street Station
This is the sub basement of Surgical Block. Here you can gain access to three service corridors that lead around the hospital

heading down the right hand corridor

heading towards Centre Block

It would be impossible to gain access to all the locked doors and dunnies due to the sheer scale of the place. Here’s a typical example of one of the many rooms along the corridors

heading along the middle corridor

halfway along there's an exit to Wishart Street

here's a route from the middle corridor that leads to the Nurses homes

you have to round past an old lift then up these stairs

back along the middle corridor there's evidence of rail tracks
the end of this corridor converges with the right hand corridor

along the right hand corridor
pretty uninteresting this one

this section is accessed from the sub basement below Medical Block
I found this area the most interesting as the likelihood of a tunnel leading down High Street would be located here


Well couldn’t find any evidence of hidden tunnels but as stated the scale and access makes it impossible to be 100% certain, however there were no locked rooms below Medical Block