Unfortunately, the castle is in ruins, in no small part due to the events of 1859, when the castle was partially blown up by skiving schoolboys who were continuing gunpowder experiments they had learnt in chemistry class at the nearby Portora Royal School. They also tried to dig underneath the building, which undermined its foundations. However the ruins are still impressive, and give a sense of the scale the building used to have.
There is a pleasant walk from the castle to the school grounds, heading South East along the river where you will pass the recently refurbished Portora Rowing Club boat houses. At the end of the path, you will also come to the site of the old Portora School swimming pool, now sadly filled in - but where Bert learnt to swim! :)
The cache has had to be replaced and is now a bottle-top type with no room for swaps sadly.
For parking, take the lane off the A46 marked for Portora Castle - there is ample parking beyond the houses, at the given coords.