The well-travelled Dutch writer Cees Nooteboom was looking for a place in Munich where he could drink a glass of champagne to celebrate the arrival of spring.

He chose a fish restaurant called Poseidon, sat down and, although he was in the middle of writing a book, within a few minutes had decided to post some letters to the god of the sea.

He asks Poseidon what it's like to be a god, what the gods thought about life on Earth today, and whether Poseidon and his pals still even existed.

He writes to Poseidon from several places in Europe and elsewhere he is accustomed to visiting in the course of his year. (By the way, Nooteboom makes a good case for using Poseidon; granted that was his name - "ground shaker" - before the Romans made off with the pantheon and started fooling around with it. But Neptune is a nice name too, and to some ears it sounds a little deeper.)

Nooteboom chides Poseidon for never writing back, and yet the letters start to sound like a correspondence, as the author gets more and more wound up by this and about some of Poseidon's mistreatment of mortals and immortals. In a café in Buenos Aires, Nooteboom has been brooding about Poseidon's lusts.

A big fellow gets up and leaves, revealing a girl reading a book in the window. This makes Nooteboom flip. "You would have wanted her and had her, just as you had everyone you wanted, Alope and all those others. Even if you had to change yourself into a stallion to do so…" he seethes.

Collections of apercus and pensees can be hard on the reader. Pascal set the tone for this kind of book - he's interesting, if a little long-winded about God. Pessoa is pretty hard to take. Nooteboom is a writer of almost everything - poems, stories, novels, travel. The trenchant materials for this book could of course have been shaped into poetry or used in fiction.

The lack of formal structures, that usually help the reader to understand and remember a work of art, means you have to keep paging back to refresh your memory: books of this sort don't build.

Also, you get the idea the publisher said the letters to the god aren't enough, throw in some other stuff. So Nooteboom did, going off on some albeit very pleasing tangents. A man was allowed by special dispensation from the President of France to marry his partner after her death (she was represented by her hat at the ceremony). Nooteboom wonders if it recognised old friends. He ponders on the shape of the famous cloud rendered by the explosion of the Challenger spacecraft.

He cogitates on what is known as the "blood moon" in Spain and - this is very refreshing - in building on this astronomical lore he starts to consider the thorny problem of the expansion of the universe.

He takes us along a bit of the way in current thinking, but then stops and admits that it's beyond him. Now when was the last time you heard a writer discussing science suddenly and plaintively bleat that it's too complicated, that it's doing his head in? Mr Bragg and Mr McEwan, I'm talking to you.

But given the respect and knowledge and regard given to the god of the sea by the novelist, it seems that many of these subjects could have been inserted into the letters themselves. There's a piece about a visit to Les Invalides - old Poseidon would probably be pretty interested in a chap like Napoleon, no? Why not?

As in the novels of WG Sebald, Letters To Poseidon is illustrated with some photographs and historical documents, some of which are representations of Poseidon in art through the ages. They're interesting, but without them the book would have been more elegant.

At one point Nooteboom amusingly asks Poseidon if he's ever done much reading, particularly about himself and the other gods.

Hieronymus of Rhodes, he says, claimed that when Pythagoras descended into hell he saw Hesiod bound to a post, howling in agony, and they'd hung poor old Homer up in a tree with a lot of snakes all over the place. (Despite his reviews.)

This is what you get when you say too much about the gods, or maybe even anything about them. "It is the ultimate in censorship," Nooteboom writes to Poseidon. "And it happened even though we know that all the tales about your scandalous lives are true. These are not the lives of saints. Adultery, revenge, lust, betrayal on the battlefield, rape, patricide, perhaps that is why you remain immortal." Palmy days.