What a lovely little city!
I found Ljubljana to be a lovely little city with the atmosphere of a village. Its small size allows everything to be easily reached on foot. Although the sights in the city centre can be visited in one day, its pleasant atmosphere, its central location in Slovenia in combination with the very good public transport connections make Ljubljana a place to stay longer than just a single day. A small warning: if you're looking for a bargain destination, then you're in the wrong place.