Jason Raad from First Bergvliet Sea Scouts in Cape Town built this tower as his Springbok construction project. It's a spiral staircase, anchored around a central flagpole. All of the uprights are firmly bedded in the ground, set into holes made with a post hole auger.
This tower draws some inspiration from a similar tower built by one of the Finnish troops at the recent World Scout Jamboree, where Jason was in my troop. The planning model is finely detailed and worth a look in it's own right.