Below photos show our approach towards Diamondhead crater on Oahu. We took the bus from Waikiki and then climbed a hill towards this tunnel. That's the rim of the blown out crater with a car tunnel going through. Pedestrians have to walk through the tunnel on a 2-lane road with tour buses. It's commonly done, and there's a bus stop right there to disgorge tourists ready to brave the road on foot.
Below is view while walking through the tunnel.
Here's what we looked like fresh off the bus. Still calm and collected (before seeing the tunnel).