This bunker is based on the german Regelbau C-1 machine gun emplacement, it is scaled up to accommodate a 60mm based weapon team inside. If you want a more realistic size in 28mm 1/56 scale reduce width and depth to about 60%, leave height.
I gave the walls a concrete looking texture buy adding some watered down filler/spackle on the printed bunker. Then spraypainted and finished with some heavy drybrushing.
Should print fine without support.