Of a compact size and shape, it is one of the oldest University cities in Europe and a UNESCO world heritage site. It's busy but with so many places to wander around, not too crowded. Easy walking, places to sit, cafés, bars, etc. enable you to spend all day exploring and not be too tired to eat in the evening. Be aware, though, that most restaurants don't open for dinner until 8.30ish!
Where to stay? There is a good choice of hotels, starting from under £40. For luxury, fly-drive for a 3-night stay in the Hotel Rector in the heart of Salamanca or, for a family holiday with children, take the 24-hour car ferry to Santander (it's like a mini-cruise) and drive the 225 miles to Salamanca, which is a fairly pleasant three and a half hours, then stay in a self-catering wooden chalet at the Hotel Regio. It's a short drive into the heart of the city and there are car parks around its edge - or - take the bus from the hotel into the city centre for under a Euro per adult. Salamanca is one of my favourite cities!