Map Undergraves by Kevin Gwartney - how to get Gold Key ???

Someone have been played this map ?

https://www.quaddicted.com/reviews/gunman02.html

I can’t get the gold key without cheating !!!. Someone says some about button semi hidden, but i can’t find this button.

I have 36 old years and still play Quake !!!.

http://s006.radikal.ru/i215/1405/da/e1857bfa56f8.jpg

Thanks !!!