This was photographed in the Waitomo worm caves of New Zealand. The blue lights are actually glowing worms and required nearly a 2.5 m exposure time at F2.8 and ISO 1600. I used a Nikon D810 with Tamron 15-30 f28 lens. The trickier part was having my wife stand perfectly still as she waved a flashlight during the long exposure to illuminate the back of the cave. I think in the end it was 20 seconds that sealed the proper exposure. This shot took almost an hour as each "experiment" took almost 3 minutes to try, then review, and reshoot. Well worth it though.