The inspiration for both Pike and Maleficent's castle looks like Tintagel in Cornwall. The site is in ruins today, but there are a few aerial pictures of the site that give you a good idea of what this would have looked like: 1, 2, and 3. It was a castle built on a rocky outcropping of land off the shore with a very narrow pathway as its only entryway. The site was built on between 400 and 700 AD, then abandoned, and a chapel and castle were built on it again by the Normans in the very early 1100s. There are other castles on outcroppings like Conwy Castle that u/VonSchneiderman pointed out and Lichtenstein Castle as an inland example, but I would still lean toward Tintagel as a more direct source because of its special claim to fame in literature.

As you can see from the pictures, Tintagel probably didn't exactly fit the "scary castle looming on an outcropping" motif perfectly in the same way the more dramatic examples in modern fiction do, but Tintagel was an example made famous by Arthurian legend. In the most famous examples of Geoffrey of Monmouth's Historia Regum Britanniae (ca. 1136, meaning Geoffrey probably saw his contemporary Castle Tintagel) and the later medieval Thomas Malory's Morte Darthur (ca. 1469). The stories vary, but I'm going to stick closer to Geoffrey of Monmouth, since it includes more relevant information about the castle. Tintagel is one of the castles held by Gorlois, Duke of Cornwall. There are variations on the story in different sources, but in all cases, Gorlois has a famously beautiful wife named Ygerna, and the two of them end up at a feast with Uther Pendragon, the king of all Britons. Uther lusts after Ygerna and starts behaving inappropriately by sending her food and longing looks at the feast, to the point that Gorlois notices, becomes furious, and leaves the feast with his wife and men without being given leave. Uther takes that as an insult and goes to war with Gorlois.

Gorlois puts his wife Ygerna in castle Tintagel while he himself takes up a separate defensible place. While Uther besieges Gorlois, he gets overcome with "love-sickness" and calls for his men to figure out a way to satisfy his "love" for her, lest he have a breakdown. This is tricky, as one of Uther's advisors points out how strong Tintagel is:

"no power on earth can enable us to come to her where she is inside the fortress of Tintagel. The castle is built high above the sea, which surrounds it on all sides, and there is no other way in except that offered by a narrow isthmus of rock. Three armed soldiers could hold it against you, even if you stood there with the whole kingdom of Britain at your side."

Brute force being useless, they turn to a famous prophet named Merlin. They summon Merlin, who has "certain drugs" or a potion to make Uther look like Gorlois so he can waltz right into Tintagel and get to Ygerna, who will think Uther is her husband Gorlois. The plan goes smoothly, Uther rapes Ygerna, and Gorlois conveniently gets killed in battle that very night so that Uther can safely marry Ygerna before she gives birth to a young boy named Arthur.

Geoffrey of Monmouth's text was a medieval bestseller--we have many, many copies of it leftover today, and it sparked the whole literary tradition of King Arthur that took off in courtly literature all over Europe. Tintagel was right there at the beginning of it all as the site of Arthur's conception, so it's easy to see how the theme of "big impenetrable seaside castle" can translate easily into other works of fiction. Because naturally, if you can't take a castle by brute force, it's that much easier for an author to make it a plot device. I can't say beyond a shadow of a doubt that GRRM and Disney were drawing on Tintagel for inspiration, but GRRM does draw heavily on his idea of medieval European history for his books, and Disney's Sleeping Beauty drew on medieval aesthetics in its animation and artwork, so the fictions are at least close in proximity with each other.

Sources:

• The History of the Kings of Britain by Geoffrey of Monmouth, trans. Lewis Thorpe for Penguin Books (the academic Latin version is a little different, but this is the translation most university courses I've seen will ask for, and it's by far the most accessible in terms of language and price)
• "Tintagel Castle" by Charles Thomas, an article in Antiquity that features an even better aerial view of the site
• English Heritage has a convenient and reader-friendly but less strictly academic resource on the site

The inner keep of Conwy Castle, in the walled town of Conwy, is constructed atop a sheer rock outcropping that stands 40 Feet above it's surroundings. With it's largest drum tower being over 50 feet tall, the keep has a commanding view for miles across the plains of North-Western Wales and the Irish sea to it's rear.

The castle's construction in the 12th century was an engineering marvel and stood as a strong statement for Edward I's political influence (many of the lead architects were blatantly poached from the courts of his enemies), and dedication to his life's work of subjugatiing the Welsh marches.

During the English Civil war, the then-500 year old castle was wrestled from Royalist posession and ordered to be demolished - depite the majority of Parliamentarian cannon being called in to destroy the walls, the stone foundations were impervious to shot and demolition plans were abandoned.