The Colour of Magic.
Begin at the beginning.
A world on the back of a group of elephants, riding a turtle, who swims through space. On a world like that anything can happen. And in the Discworld, anything does happen.
The first book in the hugely successful Discworld series introduces the Great A'Tuin as a backdrop for Terry Pratchett's mockery of the fantasy genre. Yes, there is a powerful wizard. Yes, there is a mighty barbarian hero. Yes, there is a damsel to be rescued. And if that was the end of it, it would be like a thousand other fantasy novels that no one will ever read. But the powerful wizard, Rincewind, knows one spell, that he doesn't control and is abysmal at performing any other magic. The mighty barbarian hero, Cohen the Barbarian, is older than my grandmother, and ten times as mean. And the damsel to be rescued is more than capable of handling things herself if the need arises. Wait, I'm missing something. Oh yes, the tourist. The world's first tourist, who keeps his rose colored glasses clean through out each misadventure.
Admittedly, this is not my favorite Discworld novel. Others have a more polished feel, with greater depth of character and world-building. But it is a wonderful introduction and a read in conjunction with The Light Fantastic, it makes a fun adventure.
A small British studio, The Mob, with Sky One, took a shot at a two part TV movie in 2008. While it received mixed reviews by critics, the fans, myself included, loved it. It was great to see the world I had read so much of come to life in such a vivid and realistic way.