Guam's Mount Lamlam technically world's tallest mountain, though most of it is underwater
No need for oxygen tanks and a trek to the Himalayas to climb what might be the tallest mountain in the world.
Mount Lamlam on Guam — just 1,332 feet above sea level — is another 36,070 feet from the bottom of the Marianas Trench, roughly 200 miles below. By contrast, the peak of Mount Everest — if placed at the bottom of the trench — would still be 6,000 feet under water.