In reply to mike steele:
Don't think it's a very good idea to climb these lower slopes of Eiger: too dangerous, lots of rubble and rockfall. Once you make it to Stollenloch (which is different from the windows where the train stops!!!), it is rather unlikely that one of the trains will pick you up.
Two years ago, I climbed a rock route starting from Dynamitloch which is about 200m before Stollenloch. We couldn't arrange being dropped off there by the train, so we just walked through the tunnel, early in the morning long before the service started. It is strictly forbidden to do so, but nobody was around and noticed. So it is up to you to take the risk of being caught.
Because we did not make it to the top of our intended route (which is a 20 pitch 7c+ adventure), we retreated by abbing and went back into the tunnel. By then it was late afternoon and the trains were in service. However, they did no let us in. Hence we just walked down the tunnel. While my friend just took the regular exit at Eigergletscher, I chose the alternative low-profile exit where you end up in the middle of the Via Ferrata that leads to Rotstock. Nothing happened to either of us. While I didn't encounter any further trains while in the tunnel, my friend passed 3 more trains going upwards. There is not a lot of space on the sides of the tunnel, but enough for letting the train pass safely.
So using the tunnel (on foot) is possible, but completely at your own risk.