Mount Everest gets all the credit, but Hawaii's Mauna Kea (an idle volcano that's been around for, you know, a million years) is technically the world's tallest mountain. Technically. While it stands 13,800ft above sea level, more than two thirds of the hill is actually submerged underwater, which brings the total height to 33,136ft.
Best part of that mathematical sleight of hand is that you can get to the top of Mauna Kea without training, oxygen masks, or even having to ask a dude to carry your fanny pack. All you have to do is sign up for this tour and hop on a mini-coach.
After getting learned on the island's geology and enjoying a delicious lasagna dinner, you'll make the half-hour drive up a steep incline to Mauna Kea's (which means, "White Mountain", btw) peak. Temps at the top hover around 30F, so you'll be provided with an Arctic-style parka.
Though it's cold up top, the sky's clear for around 325 nights out of the year; chances are good you'll get an unspoiled view.
Which is why it's no surprise to find 13 of the planet's biggest optical, infrared and submillimeter telescopes up there.
You clearly don't need a telescope to soak in the spectacular sunsets, though. Actually, that would be a terrible idea. Didn't you learn anything in physical science class?