Iwo Jima

There are still a few pillboxes, cave openings, gunnery installations etc that have been left in memorial to the battle. You can go into a few of the caves however most of the deeper and more complex caves have been blocked off. Mt Suribachi is riddled with caves that Japanese troops used as shelter and defensive postions during the battle. Those caves have been blocked off since many of their bodies were never recovered after the war and the mountain is essentially their grave. Plus there is still thought to be several remaining ammo stockpiles that were trapped in those caves so they're not safe to explore.