As an ex - maintenance worker for the University, I can say that this entrance leads to under ground rooms ( located beneath Woodland Road ) used for telecommunications in WW2. ( as were quite a few of the buildings in Woodland Road, 19 and 21 especially.) Later used by the Post Office GPO telephones. In the late 70's there were still old fashioned switchboards in place. The rooms were later used for teaching purposes but this ceased due to fire regulations ( insufficient escape routes ). The rooms can also be accessed by another entrance in the cellars of No. 11 Woodland Road. I was last in there shortly before they were bricked up, badly flooded and used by youngsters.
There was also discovered an ARP room in the basement of No.8 ( The building adjacent to above mentioned bunker ) this was found intact containing many interesting items which sadly swiftly disappeared, great coats, gas masks, cardboard coffins and emergency plans Etc. which I was priveleged to see. There were even tea cups and a copy of the Daily Mirror from the war years on the table.
Not sure if anyone has mentioned the Anti Aircraft bunker in the front garden of 21 Woodland Road, you can still make out where a barrage ballon was tethered and for anyone interested in WW2 sites there is still evidence of Anti aircraft gun enplacements at the rear of the old Homoepatic Hospital, you can see the circular steel tracks that the guns traversed on.