There's a reason Falljökull means the "Falling Glacier." Crashing down over hundreds of years on its way from Vatnajökull National Park to the Atlantic Ocean, it is literally a giant frozen waterfall cascading decade by decade, millimeter by millimeter in front of your eyes. It also happens to be an incredibly accessible outlet glacier, which means (depending on the time of year you visit) you'll have ample opportunity to strap on some crampons and do a little glacial exploration of your own.
Half-day (5 hr) guided treks up Falljökull typically run between $100-$125 USD, following in the true Icelandic tradition of nothing coming cheaply (little joke there). We'd highly recommend not skimping, however, since there are real dangers once you get up on the ice, including crevasses and moulins that could easily prove fatal. For the price, you'll have the opportunity to check out some cool transient ice caves, take a drink from a natural stream of glacial melt, and spend a few hours hiking up and along the giant frozen waterfall itself. It doesn't hurt that the views are pretty spectacular, too. If you're pressed for time but still want to experience some Icelandic glacier trekking, consider this a great option.
Note:Check out our links for some suggested tour options.