I liked it when my players starting crying railroad because in order to get ot the top of the tower they "had" to recover 4 items spread through the other levels of the tower.
They started crying "railroad". I said, "Yeah, its horrible that the guy (high level NPC wizard, module author, you pick) actually made it impossible for low level nobodies like you to get in without doing it the way he designed for you to get in."
To me, Railroading is done by the DM, and it is when the DM allows only "one way" to work. No matter how good other ideas may or may not work. Unless, like in my example from Goodman Games "Mysterious Tower" DCC ( DCC 3, I think), the adventure scenario is designed to be hard for anyone to get in, that is low to medium level, anyways.
Its not a crime for a wizard (or DM) to try and design something with only one way in. Especially if they were good/smart enough to do so. Especially for the lower levels. Why avoid designing such impenetrable places just to avoid being called a "Railroad". So what if it is? As long as it is fairly designed and built, your not supposed to like the "ride", but if you want to get to point "B", then you better ride the "train" until it gets there.
So only when the DM says, "No, that doesn't work." and it does, or could, is it railroading that players can cry about. That I'll listen to anyways.
If they are such babies that they cry about the DM or NPC being able to design something that actually challenges them, makes them come up with new ways to accomplish things, or dares to force them to collect 4 keys to get in, too bad. They can either get over themselves or they can DM.