Spain is large and there is much to be said for taking a holiday which includes visits to gardens, rather than attempting a full tour. Spain was inhabited by Celts before the Roman conquest. It then became part of the Empire and a country of many gardens. Arab invaders brought Islamic design ideas. In the twentieth century Barcelona became famed for modernista (Art Nouveau) and then for modern design. See list of gardens to visit in Spain.
Many tour companies take visitors to Spain but the country has a very large tourist industry and is comparatively easy for the independent traveller: there are many hotels, the trains and buses work well. English is widely spoken in the holiday areas but not elsewhere. Garden holidays and tourism are most comfortable in spring and autumn.