I concur with Barney and Wittmann – the design doesn’t make me think of A&A or even of WWII.
One idea might be to look for pictures of Atlantic Wall fortifications and try to find one that actually was a cliffside bunker. Pointe du Hoc (the cliff famously climbed by the US Army Rangers on D-Day) had fortifications at its summit, and the Batterie Lindemann guns would be another option. This website–
http://bunkersite.com/locations/france/calais/sangatte/leit-sangatte.php
– has lots of pictures of WWII German bunkers, for example the one below. Your friend could take elements of different pictures (a cliff, a bunker, and a heavy coastal gun) and combine them, if no single picture is ideally suited.