What is a guesthouse? The obvious answer that it's a sort of accommodation for the guests. But speaking of details, in different countries different hosts understand this word differently. For some of them it's only a question of name: you call a hotel and it becomes a guesthouse.
The term of a guesthouse lays somewhere between a hotel and an inn. Guesthouses all around the world are quite various, still they generally have some common features.
A hotel is something more official, more public if you want. A guesthouse tends to be more like a home. It's never too big, never too crowded. The personal is friendly, not friendly because it's their job to be friendly and nice with guests but because they really are. Or this is how it's supposed to seem. Sometimes and in some countries even more likely guesthouses are family-run - that is one more source of the warm atmosphere.
Guesthouses may be called an alternative to hotels. A cheaper one, although not always. In some of them you'll have to pay a good deal of money for feeling at home. Also one may call guesthouse - the B&B turned into the general business. All the borders between these accommodation definitions are rather vague.
Guesthouses by the number of room vary from very small to medium. This means that one building may contain from five or about that to thirty rooms. The conditions of stay aren't the same in all guesthouses. Mostly the charge includes the breakfast and all the facilities like local phone calls, car parking and etc. The guesthouse accommodation is rather various. All of them will offer you classical twin, double and single rooms with private bathrooms. Some also dispose of multi-room suites for guest travelling in company or for large families. Multi-room suits will probably mean for you one shared bathroom on the floor.
In some cases you will find a basic kitchen in the room which means a kitchen range and a small refrigerator - so that you can cook yourself some simple hot snacks. Nowadays almost every guesthouse room (probably except for those in the very exotic countries) is provided with color TV and heated in the winter time.
You may choose a guesthouse situated in the center of the city not far from all the main bus-routs and historical sights. Some hosts even meet their guests at the airport and transfer them to the place. The same thing with the departures. This option is very convenient minding that you are probably coming to the city for the first time and know nothing around.