F'ing Awnings!
I went to a mates 50th in Amsterdam and had got a very detailed headmap of where the pub I was to meet him in was. Couldn't find the bugger. Went back to my hotel and checked directions and set off again still couldn't find it. Then I bent down and looked under an anonymous awing to see the pub name beautifully etched on the windows invisible to anyone more than 4 feet tall.
Strangely I could read it when I left!