Lyonesse

Lyonesse is a sprawling fantasy trilogy by Jack Vance, comprising three volumes:

Lyonesse (aka Suldrun's Garden or Lyonesse: Suldrun's Garden),
The Green Pearl (aka Lyonesse: The Green Pearl), and
Madouc (aka Lyonesse: Madouc), winner of the World Fantasy Award in 1990.

The series is set on the mythical lost great isle of Hybras, located off the coast of France, between Britain and Spain. The isle is divided into several kingdoms, and three kings want to rule it all. Aillas, the youthful king of Troicinet is shipwrecked on the coast of Lyonesse, where he meets and falls in love with Princess Suldrun, the daughter of his rival, King Casmir. Things don't go well for the couple, and their child, Prince Dhrun, ends up stolen by fairies, while the changeling, Madouc, left in its place, gets adopted by King Casmir, who believes she's his granddaughter. Then the story branches off into a complex web of interlocking tales, involving Royal ambition, nefarious wizards, tricksy fairies, and northern barbarians.

Tropes used in Lyonesse include:

Affably Evil: The prologue includes a tale of how a saint tried to convert an ogre to Christianity. The ogre politely agreed to hear him out.

Elric expounded, recited Scripture and sang the glories of the Faith. When he came to an end and declared his final "Hallelujah!," Magre gave him a stoup of ale to ease his throat. Sharpening a knife he complimented Elric upon the fervor of his rhetoric. Then he smote off Elric's head, cut, drew, spitted, cooked, and devoured the sanctified morsel with a garnish of leeks and cabbages.

Another Dimension: There is a long section set in Tanjecterly. It's a strange place where trees are different colors, and the heroine is menaced by grotesque, slime-eating creatures called Progressive Eels.
Atlantis: The beginning of the book explains that Hybras will sink into the ocean some time after the current story. The name Lyonesse comes from a legend of a land near Cornwall that sank beneath the waves. Likewise, the City of Ys also comes from a legend of a city near Brittany that also sank into the sea. Finally, the name Hybras itself is reminiscent of Hy-Brasil, a legendary disappearing island near Ireland.
Bad Luck Charm: The Green Pearl features the eponymous item which will turn anyone who owns it to evil, until somebody else murders them to possess it. At one point the chain is broken when the owner is rendered helpless by somebody who's only interested in punishing him, and the pearl is temporarily forgotten.
Changeling Tale: Princess Madouc is a relatively innocuous example.
Clingy MacGuffin: The aforementioned green pearl is so beautiful that it fills the hearts of everyone who sees it with greed. Unfortunately, the pearl is cursed: no-one will buy it, and if thrown away or given away it will always return to the current owner (even if it has to animate a corpse to carry it back). It can however be transferred by being stolen, which half the time involves the murder of the current owner.
Dating Catwoman: Aillas falls in love with the haughty viking-like maiden Tatzel while being a slave at her father's castle. He escapes, comes back as a warrior king, kidnaps her and undergoes many adventures together with her, saving her life several times. Throughout he acts as the perfect gentleman, not taking advantage of his power over her. At one moment she actually offers him sexual favors in exchange for her liberty - but Aillas, wanting a love she is unwilling and unable to give him, declines the offer and sets her free anyway. Finally, when Aillas brings his army to assault the castle, Tatzel takes up a bow and arrow and dies among the last-ditch defenders. The victorious Aillas sadly refuses to look for "the body of the valiant maiden" among the scorched bodies in the ruins of the castle, and goes on to find another and more rewarding love.
Decoy Protagonist: The trilogy begins with the birth and upbringing of the spirited Princess Suldrun. At about the halfway point of book one, however, she dies. The rest of the series divides its focus amongst a number of other characters, including her lover, son and father.
The Fair Folk: They aren't downright malicious, but tend towards the whimsical in negligent or destructive fashion. Fear to tread...
Fantasy Counterpart Culture: The aristocracy of Lyonesse seems to be vaguely Germanic, Dahaut is pre-Revolutionary France, and the Ska are based on the Vikings. Troicinet represents Britain. All of these are based not so much on modern images of these cultures as on representations from the 19th century or earlier (Troicinet is a sea power and balances the other nations; the Ska aren't noble warriors but fearsome and heartless raiders, similar to portrayals of Vikings in mediaeval English sources.)
Go Mad From the Isolation: King Casmir imprisons Prince Aillas at the bottom of an oubliette. Aillas gradually loses his sanity and starts thinking of the skeletons of former inmates as friends and comrades in adversity. He gets better after escaping.
Magic Feather: The boy Dhrun is given a talisman to avert fear, which in fact means that whenever he feels afraid, he misinterprets the emotion as anger and is able to be brave. The talisman eventually gets broken and replaced with a regular stone, but it continues to work until he realizes the replacement.
Medieval European Fantasy: Lyonesse has a style similar to classic Arthurian romance, full of deliberate anachronisms.
Royally Screwed-Up: The king of South Ulfland's single son, Prince Quilcy, is feeble-minded and spends his days playing with fanciful doll-houses.
Suddenly Always Knew That: Aillas never comes across as someone particularly interested or skilled in swordsmanship. In The Green Pearl, however, he encounters an infamous bandit leader from a very martial culture who considers himself virtually peerless with a blade in hand. Out of nowhere, Aillas hands him a Curb Stomp Battle without breaking a sweat. A few chapters later, a bystander comments that he's a "demon with a sword."
Tailor-Made Prison: In Suldrun's Garden, Aillas is lowered into an Oubliette ("a bell-shaped cell fourteen feet in diameter and seventy feet underground"). Taking months, he constructs a ladder from the bones of the previous occupants, and escapes.