Schwarztor (Porta Nera) is a col at 3731 m. between the ridge of Breithorn and Pollux. You can reach it in about one hour from Klein Matterhorn using skins or simply pushing your skis: to reach the col you must gain a few dozens meters of elevation. The first part of descente is on a glacier with crevasses, then you reach an area of seracs really scenic which obliges to short turns and sometimes to use a rope. Afterwards you reach an area of moraine before reaching the large Gornergletscher. The exit is thru a small canyon as for Untergletscher skirun. The Porta Nera run is quite popular, neverheless requires experience and equipment (harness, shovel, probe, transceiver, rope). Take a guide if you have any doubt!