Lodging in Heidelberg

Not exactly sure what you mean by "back door". In Heidelberg, that would imply the cheap student apartment housing, which usually have their access doors in the back alleys... is that what you had in mind? If not, the only hotel I can personally vouch for in Heidelberg is Hotel Holländer Hof. The location and view alone should be good enough selling points, but it's also surprisingly inexpensive, if not exactly budget, and the rooms are also quite large.