Unfortunately most of it was blown up in 1811 by French soldiers during the Guerra de Independencia (Napoleonic Wars). This, along with the slaughter of the townspeople, was in revenge for an ambush of French troops by some Alcalá guerrillas the previous year. All that remained was the keep (known as la torre de homenaje in Spanish).
The keep was declared a site of historical interest in 1984, but remained basically a pile of rubble until restoration work began in 2005, using European Union funds and administered by the Diputación de Cádiz. Work continued in four stages until it was finally completed earlier this year. Although based on the original layout, there was too little of the structure left to restore to its former state, so modern features have been incorporated.
The grand opening took place last weekend, coinciding with Alcalá playing host to the Feria de Ecosistemas y Bosques de Cádiz, with guided tours and theatrical dramatisations for children and adults.
The castle building won't be left open to the public on a daily basis, although you can walk round it and enjoy the views. Anyone interested in a guided tour should contact the town hall (tel. 956 42 81 48 or send a message via their Facebook page
For some great photos of the castle and this weekend's activities see Pedro Martin's blog Alcalá a través de mi objecto.