James Malislewski talks about solitaire adventures here. One of the oldest if not the oldest soltaire for D&D was Judges Guild Survival of Fittest.
In my neck of the Woods (Northwest PA) it was respected enough that many DM would accept a higher level character that went through it. Of course you had to have a reputation for not being a cheater.
DC Adventures - 5 Bucks a Book - PDF
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