A solo adventure is one of the greatest experiences in role playing games that you can imagine. Most of the Gamemaster's focus and attention can be solely devoted to just one particular player on any given quest...like a person who sits at home to read a book by themselves, they are alone & fully engrossed within the book.
All by themselves.
The GM can 'wing it' almost perfectly & have ready any outcome that the player character could possibly conceive – be it walking along a random path in the dead of night or sitting alone, by themselves, at a table within an Inn or Tavern...drinking that day's selection of whatever may be on tap. A stein of frothy ale or a pipe full of aromatic jollyweed.