From audible.com:

In Volume 1 of the classic Gormenghast Trilogy, a doomed lord, an emergent hero, and an array of bizarre creatures haunt the world of Gormenghast Castle. This trilogy, along with Tolkien's Lord of the Rings, reigns as one of the undisputed fantasy classics of all time. At the center of everything is the 77th Earl, Titus Groan, who stands to inherit the miles of rambling stone and mortar that form Gormenghast Castle and its kingdom.

In this first volume, the Gormenghast Castle, and the noble family who inhabits it, are introduced, along with the infant firstborn son of the Lord and Countess. Titus Groan is sent away to be raised by a wet nurse, with only a gold ring from his mother, and ordered to not be brought back until the age of six. By his christening, he learns from his much older sisters that epileptic fits are "common at his age." He also learns that they don't like his mother. And then, he is crowned, and called, "Child-inheritor of the rivers, of the Tower of Flints and the dark recesses beneath cold stairways and the sunny summer lawns. Child-inheritor of the spring breeze that blow in from the jarl forests and of the autumn misery in petal, scale, and wing. Winter's white brilliance on a thousand turrets and summer's torpor among walls that crumble..."

In these extraordinary novels, Peake has created a world where all is like a dream - lush, fantastical, vivid; a symbol of dark struggle.

VOLUME II
OF AN
EPIC TRILOGY.

"It can stand with the best that has been done in the English language."
Chicago Daily News

"Shimmering nets of language capture details of an epic story." The National Observer

"Peake writes with genuine wit and a clear transparency, like a Dickens intoxicated with words, drunk with his own imaginings.  Superbly evocative."
New World

"Mr. Peake throws in all his forces of dream, vision and language."
Sunday Times

In his last visionary satire, Peake chronicles atrocities and hilarities alike with the same deadly control that never wavers

In the third of the Titus books, the seventy-seventh earl of Gormenghast exiles himself from the mad rites of his ancestral home to wander in the world at large, and discovers that in many ways it is more strange and frightening than Gormenghast itself.

Peake's lurid vision is peopled with dark and troublesome denizens: melancholic Muzzlehatch; the fading Juno; the spicy Cheeta; a galaxy of worrying strangers that inhabit the ominous Under-River; the fearful but arrogant Titus himself.

'Everything Mervyn Peake did, he did with a passion controlled and channelled so delicately it was almost frightening to experience... [he was] an artist of wit, intelligence, humanity, boundless creative gifts and a deliberately conscious, almost aggressive simplicity' - Michael Moorcock

This volume is part of a trilogy called the Titus books (also known by some as the Gormenghast trilogy).
In reading order:
TITUS GROAN
GORMENGHAST
TITUS ALONE

From audible.com:

Mervyn Peake's Gormenghast trilogy is widely acknowledged to be, as Robertson Davies pronounced, "a classic of our age." In these extraordinary novels, Peake created a world where all is like a dream - lush, fantastical, and vivid. Yet it was incomplete. Parkinson's disease took Peake's life in 1968, depriving his fans of the fourth and final volume of the series, Titus Awakes except for a few tantalizing pages, after which his writing became indecipherable. Or so it seemed.

In January of 2010, Peake's granddaughter found four composition books in her attic. They contained the fabled Titus Awakes in its entirety. Peake had outlined the novel for his wife, Maeve Gilmore, who had at last finished Peake's masterpiece.

It starts with Titus leaving Castle Gormenghast. Peake wrote: "With every pace he drew away from Gormenghast mountain, and from everything that belonged to his home. That night, as Titus lay asleep in the tall barn, a nightmare held him." Fans of Peake will delight in this new, wonderful novel, published 100 years after his birth, every bit as thrilling and masterfully written as his famed trilogy.

Listen to the Gormenghast Trilogy.