Carlow Castle has a large rectangular three-story limestone keep with circular towers at each angle. The castle dates from the early 13th century. It was built by William Marshal the elder in the time period between 1207 and 1213 which he spent in Ireland. The castle in Carlow was the very first of its kind in Ireland.
The castle was handed over to the crown in 1306, granted in 1312 to Thomas Plantagenet, confiscated by the crown in 1537 as the landlords were absent, bought by the Earl of Thomond in 1616, changed hands multiple times until it was taken by Oliver Cromwell in 1650 but was later returned to the Earl of Thomond. In 1814 the castle was widely destroyed in an attempt to create more space for the conversion into a lunatic asylum with the help of explosives. Just the outer face of the west wall and the two neighbouring towers could be preserved.
Glimmingehus is the best preserved medieval stronghold in Scandinavia. It was built 1499-1506, during an era when Scania formed a vital part of Denmark, and contains many defensive arrangements of the era, such as parapets, false doors and dead-end corridors, 'murder-holes' for pouring boiling pitch over the attackers, moats, drawbridges and various other forms of death traps to surprise trespassers and protect the nobles against peasant uprisings. The lower part of the castle's stone walls are 2.4 meters (94 inches) thick and the upper part 1.8 meters (71 inches).
Construction was started in 1499 by the Danish knight Jens Holgersen Ulfstand and stone-cutter-mason and architect Adam van Düren, a North German master who also worked on Lund Cathedral. Construction was completed in 1506.
Ulfstand was a councillor, nobleman and admiral serving under John I of Denmark and many objects have been uncovered during archeological excavations that demonstrate the extravagant lifestyle of the knight's family at Glimmingehus up until Ulfstand's death in 1523. Some of the most expensive objects for sale in Europe during this period, such as Venetian glass, painted glass from the Rhine district and Spanish ceramics have been found here. Evidence of the family's wealth can also be seen inside the stone fortress, where everyday comforts for the knight's family included hot air channels in the walls and bench seats in the window recesses. Although considered comfortable for its period, it has also been argued that Glimmingehus was an expression of "Knighthood nostalgia" and not considered opulent or progressive enough even to the knight's contemporaries and especially not to later generations of the Scanian nobility. Glimmingehus is thought to have served as a residential castle for only a few generations before being transformed into a storage facility for grain.
An order from Charles XI to the administrators of the Swedish dominion of Scania in 1676 to demolish the castle, in order to ensure that it would not fall into the hands of the Danish king during the Scanian War, could not be executed. A first attempt, in which 20 Scanian farmers were ordered to assist, proved unsuccessful. An additional force of 130 men were sent to Glimmingehus to execute the order in a second attempt. However, before they could carry out the order, a Danish-Dutch naval division arrived in Ystad, and the Swedes had to abandon the demolition attempts. Throughout the 18th century the castle was used as deposit for agricultural produce and in 1924 it was donated to the Swedish state. Today it is administered by the Swedish National Heritage Board.
On site there is a museum, medieval kitchen, shop and restaurant and coffee house. During summer time there are several guided tours daily. In local folklore, the castle is described as haunted by multiple ghosts and the tradition of storytelling inspired by the castle is continued in the summer events at the castle called "Strange stories and terrifying tales".