Built in the XV-th century on a cliff above the Zlaşti stream, the castle of Corvin Family (hu.: Vajdahunyad vára) is the most important gothic monument from Transylvania, and one of the most imposing structures in Romania. Placed in a mining zone, in the town of Hunedoare, the castle got blackened and dirty but the main polluting factories are now closed and the castle is being restored (and I had the misfortune of visiting it during this period when not every section of the castle was opened to the public).
There isn't much to say because there is plenty of information on the internet and you could check out some of the following links: the official site, Wikipedia, Travel Romania or here.
Some of the main attractions of the castle are: the drawbridge, the Last Defense Tower (Ne boisa), the Capistrano tower, the Council Hall, the Knight's Hall, the Club Tower, the White Bastion, the Diet Hall and the 30 meter deep well.
The location is this, and some personal photos follow: