I am typing this as a person who did not actually know Thermopylae Pass by name but almost certainly by sight as I covered all of the Hill during my youth. I spoke with the Rangers at Tam O'Shanter's Cottage, opposite Flaybrick Cemetery, and they told me this was what is now Upton Road going down Ford Hill. What brought this topic to the fore was an email conversation with a lady in Australia, Joan Grey, who knew this Pass very well. I told her that there was nothing on the internet about this, nor does Google maps show anything. I thought it was just a local nickname as opposed to a geographical feature. I have had some information (June 1024) from George Girven, Birkenhead, who tells me that parts of the Pass do still exist. He provided images but they were too dark to see anything. Thanks George.
I have the following information from Joan Grey, now in Australia:
I can't believe that they have disappeared Thermopolyae Pass, when I was a child this consisted of a wild hilly area, with masses of gorse in the summer and wildflowers. It was a great place to play hide and seek. One summer we turned up there and houses from the Noctorum Estate had suddenly appeared at the bottom of the hill taking up part of the Pass. We were flabbergasted even then but didn't know who to complain to, if at all. I am sure Thermopolyae was part of the original deed of covenant with Bidston Hill. The house on the right of the image above was a country property and the grandparents of a friend lived there as caretakers I think, I am sure they didn't own it. There were stables attached to this property, you could stand at the top of the road and look over the Pass and down towards the house and stables. It was the most beautiful vista. I think this house has now been demolished. Regards, Joan (July 2010).
Joan also found this information that may lead to where the Pass is/was?
'From Tam O'Shanter cross the field south, then left along the King George Way to the park entrance. Cross over Upton Road and follow Bidston Road past the Wirral Ladies Golf House, turn right at the footpath sign and cross the golf course to Noctorum Lane. Follow the lane to Budworth Road, then turn right passing Noctorum Road and along West Road to West Close.
Proceed north along the footpath
opposite the close until it reaches the Thermopylae Pass, turn left and follow
the pass to near its Upton entrance. Turn right and walk up the yellow brick
path through Bidston Court gardens until reaching the terracing. Climb the steps
up the terrace to the large semi-circular walled patio belonging to the old
house (removed and rebuilt at Royden Park and now known as Hillbark).