The Sailor on the Seas of Fate by Michael Moorcock

Leaving his cousin Yyrkoon to sit on the Ruby Throne of Melnibone, Elric leaves his home to travel the Young Kingdoms. He tells his lover (and cousin) Cymoril that he will be back in one year. Of course, Melniboneans are not very well received in the Young Kingdoms and this makes Elric's travels tough.
At the beginning of the book, Elric is picked up by a ghostly ship that sails along waters between the worlds. The ship is bound for Tanelorn and Elric soon finds that his fate is tied with other manifestations of the Eternal Champion. Together they fight and conquer Agak and Gagak, two powerful sorcerers that are also brother and sister. This part of the book is the same adventure as that told in The Quest for Tanelorn from the Chronicles of Count Brass series but is told from Elric's point of view rather than Hawkmoon's.
After the battle against Agak and Gagak, Elric decides to re-board the ship. He is later told that there is a portal to his world near an island and is taken there. As the island nears, there are corpses floating in the water and a terrible moaning in the air. Elric is hesitant but is told that if he doesn't go, he may be stuck on the ship forever...so he goes.
Once on the island, Elric encounters a group of pirates that seem to be from all different places and eras of history. They attack him and, with the help of their prisoner Smiorgan Baldhead, he defeats them. Together, Smiorgan and Elric search for the Crimson Gate, a portal back to their own world. Along the way, they find a woman, Vassliss, and are hunted down by Earl Saxif D'Aan of Melnibone who believes the woman to be his lost love, Gratyesha, Princess of Fwem-Omeyo.
Once through the Crimson Gate and back into their own world, Elric and Smiorgan are found floating in the sea by Duke Avan who is on a quest to find the ancient city of R'lin K'ren A'a beyond the Boiling Sea. Since this city is supposedly where the Melniboneans came from, Elric decides to join the quest. The events that follow set off the great struggle of the Upper Worlds.
This book was full of action and I didn't find myself bored for one minute. If you're an RPG gamer, there is also lots of great inspiration within this story.