Real homes: what makes a great guest room?

We're thinking of renting out what used to be the lodger's room on Air BnB. 



The room was decorated, years ago, with a lodger in mind – this meant plainly and sparsely, so someone else could make it feel homely.

Air BnB is, of course, a different beast. You want to inject a bit more personality, give the space some personality. (But how much personality?) So I'm revving up for a major guest