The other three bunkers are not officially open as they have been vandelised and have become unsafe.
Outside stands one of the two remaining Krupp K5 28cm railway mounted guns of which eight were made, the other remaining example is in the USA. Designed for service in the Invasion of France to support the infantry, problems were encountered with the barrel splitting that was rectified with changes to the rifling. The guns were then reliable until the end of the war, under the designation K5 Tiefzug 7 mm. Three of them were installed on the Channel coast to sink British shipping in the Channel, and unfortunately proved successful at this task.
A personal photographic note
I've heard that there has been comments about members taking 'postcards'. Well, all these shots from the Somme are my postcards, they are my personal memory jolters, the last thing on my mind was the club judge (I was one for over 30 years). Who ever made those comments should remember that the stylised competition pictures, and the navel contemplating images some independent togs make, will gather dust in the future while the family snap and holiday postcards will be looked at and talked about for years to come. Make pictures the way you want, for the reasons you want and if you win a pot or two along the way that's a bonus.