This type of gun emplacement can be mostly found in France. It can be found in huge amounts, the reason for this huge amount was probably that they thought a great number of smaller weapons is more effective than some gun emplacements with a big 8.8 cm AA gun.
This bunker normally has an accommodation for the troops. The staircases gives a quick entrance from accommodation to the AA gun. Between the staircases there is room for the gun to be picked-up and moved by trolley.
SK is Sonder Konstriction. This means that the gun emplacement has been constructed out of two or more different regelbau types.