An interesting secret place

Use Google Maps and go to the intersection of 23rd Street and Valencia Street in San Francisco.
There is a small utility access cover plate on the NW side of the intersection. It is painted yellow.
Go to the cover plate and see what is under it.

Remember
This is a secret.
/\
Don't try to take anything back with you from the Secret Cave
Don't tell anyone where you went
or
what you saw
....
If you tell, you will be savagely cursed.