CPV code 63512000 designates Sale of travel tickets and package tours services in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
63512000 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 63510000 (Travel agency and similar services).