Today, as per tradition, the 18th Duke’s duties include officiating at State funerals, investiture and coronation. The ‘Earl of Arundel’ title is used by the heir apparent.
There's more information and advice on things to look out for at the Castle on the BBC History Extra Website here and the Arundel Castle website here.
There are spectacular gardens.
The Fitzalan Chapel is situated in the white garden below and was founded in 1390 as the burial place of the Dukes of Norfolk. It is part of the Protestant Parish Church of St. Nicholas however, in 1879 it was decided that the Catholic Chapel was a separate entity and was partitioned off by a glass wall (above). A very unusual situation to have two denominations in one building.
The Catholic Cathedral, visible from the garden was built by the 15th Duke of Norfolk and is now dedicated to Our Lady and St. Philip Howard, the 20th Earl of Arundel, following his canonisation in 1971.
The gardens consist of the Collector Earl's Garden, The Stumpery, Herbaceous Borders, Cut Flower Garden, Organic Kitchen Garden, Rose Garden and a peach house and vinery and the photos below don't really do them justice.
The gardens and Dancing Crown Fountain were designed by Julian and Isabel Bannerman and were opened by Prince Charles.
There are 131 steps up to the top of the Keep from which you can see for miles.
All in all it's a wonderful place and I would thoroughly recommend a visit.