Hohenzollern Castle (German: Burg Hohenzollern)
This is one of my favorite castles to take visitors to because of its proximity to Stuttgart and because of the fun markets, festivals, and events they offer throughout the year. Events include a fall fest with regional specialties to taste and purchase, a Christmas market, and a beautiful spring floral display that spills into the interior of the castle.
Driving is the preferred method and once you arrive you can get to the top by either parking and walking the 30 min path to the entrance (uphill), or park and take the shuttle bus next to the souvenir shop in the parking lot. The shuttle runs regularly and costs 1.90 Euro one way (if you prefer to walk up or down one way) or 3.10 Euro round trip. Ticket prices, maps, and additional visitor information can be found here.