The Jungfraujoch terminus stands at an elevation of 11,333 feet; you may feel a bit light-headed from the altitude. Follow signs to the Top of Europe, a gleaming white glass-and-steel pavilion. The expanse of rock and ice you see from here is simply blinding.
If the staggering views from the terminus aren't enough for you, you can reach yet another height by riding a high-tech high-speed elevator up 384 feet to the Sphinx Terrace: to the south crawls the vast Aletsch Glacier, to the northeast stand the Mönch and the Eiger, and to the southwest towers the tip of the Jungfrau herself. Note: even in low season you may have to wait in line for the elevator.
More than views are offered to the hordes that mount the Jungfraujoch daily. From June to the middle of September, you can sign up for a beginner's ski lesson or a dogsled ride, or tour the chilly blue depths of the Ice Palace, featuring ice sculptures as well as cartoonish wood carvings and information on the Jungfrau Railways. Be careful, you're actually walking on ice. Admission to the attraction is included in the price of the excursion.
A few things to keep in mind for the Jungfraujoch trip: make sure you have great weather, as the views are the thing here. Webcams can clue you in. Take sunglasses, warm clothes, and sturdy shoes with good treads; even the interior halls can be cold and slippery at the top. Some sensitive individuals may experience fatigue or headaches from the high altitude at the top. The symptoms usually disappear on the train ride down. Return trains, especially toward the end of the day, can be standing room only.