Amadan (The Fool) by J C Milne.
This book is 575 pages long and is written in English.
 
In the morning after the night before, Alex meets an enigmatic figure who leads him into a series of time-travelling adventures to his island's Viking past and to ever more distant locations, till finally he comes full circle. In his travels he encounters real-life characters from history who have been thrown into his own fantastical situation... and is himself caught up in discovering the identity of his enigmatic companion, by means of a riddle that seems unsolvable. Within a framework of fantasy the story explores issues of human error, love, treachery, bitterness and, ultimately, forgiveness and healing. It captures the timelessness and magic of the islands of the west.