Best viewed in 'original' size, to get the full benefit of the detail. This shot was taken through a very thick glass window set into the north face of the Eiger. For more details read the following info from WikipediaÉ

"The Jungfrau is the highest peak of a mountain massif of the same name, located in the Bernese Oberland region of the Swiss Alps, overlooking Wengen. The other two peaks are the Eiger (3,970 m) with its famous north face, and the Mšnch (4,099 m). The summit of the mountain was first reached in 1811 by the Meyer brothers of Aarau.

Once difficult to access, the Jungfraubahn cog railway now runs inside the mountain, up to the Jungfraujoch railway station at 3,454 m (11,332 ft), the highest in Europe. The train into the mountain leaves from Kleine Scheidegg, which can be reached by trains from Grindelwald and Lauterbrunnen. The train enters the tunnel running eastward through the Eiger shortly after leaving Kleine Scheidegg.

It runs close behind the Eiger's north face, stopping at Eigerwand, where there is a window about 8 m long and a metre high, halfway up the face. The windows have been placed in holes used to remove excavated rock from the tunnel during construction, and are also occasionally used as access points to rescue climbers. This window was used for one of the final scenes of a Clint Eastwood spy movie the The Eiger Sanction. There one can get off the train to admire the view before the train continues five minutes later.

The tunnel then turns west, heading towards the Jungfrau. There is a second stop at a window looking out on the Eismeer ("Sea of Ice") before the train continues to the Jungfraujoch. The tunnel was constructed between 1898 and 1912; it is about 7 km (4 mi) long, with gradients of up to 25%. The journey from Kleine Scheidegg to Jungfraujoch takes approximately 50 minutes including the stops at Eigerwand and Eismeer; the downhill return journey taking only 35 minutes."