It is ridiculous to dismiss Pliny on account of his many mistakes and factual errors and so on.
The way to read this book is the way in which you read that kind of fantastic literature that gives the "illusion" of fact; Borges and Italo Calvino come to mind - the first one had plans for making an edition of Pliny in Spanish, with his prologue, but died before finishing the project (you can check the notes of Borges' Selected Non-Fictions for that); Calvino in fact wrote a wonderful essay on Pliny, included in "Why Read the Classics?", a book everyone giving "Natural History" less than four stars should read urgently.
Let's say it: if Pliny had got everything "right", he would still be used to teach natural science in high-school... and, for that reason, nobody would care about him.
There are people who think that the only documents that tell us something about the past are those written with a clinical, cold eye: the look of an outsider. This book is fun PRECISELY because Pliny wrote down everything that reached his ears without checking the facts -Zeus bless his heart-, and because of his welcoming disposition, a geography of the common imagination of that time has been preserved; something that otherwise would be lost.
Not long ago some people around this parts believed the Russians ate their own children. A good number among us are certain that paying someone to listen to your problems for fifty minutes every week, allows you to confront your unearthed traumas and clean up your life. Maybe in a thousand years all this will be just the mythology of our time. A few days ago scientists started to suspect Pluto is not a planet after all, so all those books written about it in the past century... they are mutating already into vintage science fiction.
In the meantime, how can anyone not be interested to know that "there is a record of 120 (mice) being born from a single mother, and in Persia of mice already pregnant being found in the parent's womb; and it is believed that they are made pregnant by tasting salt"(X, LXXXIV)? Or that "the day on which King Pyrrhus died, the heads of his victims, when cut off, crawled about licking up their own blood"(XI, LXXVII)? Or that "some people are born with a hairy heart, and that they are exceptionally brave and resolute. An example being a Messenian named Aristomenes who killed three thousand Spartans. He himself, when severely wounded, was taken prisoner and for the first time escaped through a cave from confinement in the quarries by following the routes by which foxes got in. He was again taken prisoner, but when his guards were fast asleep he role to the fire and burnt off his thongs, burning his body in the process. He was taken a third time, and the Spartans cut him open alive and his heart was found to be shaggy"(XI, LXIX)?
How can anyone not enjoy fragments like this one: "The most learned authorities state that the eyes are connected with the brain by a vein; for my own part I am inclined to believe that they are also thus connected with the stomach: it is unquestionable that a man never has an eye knocked out without vomiting."(XI, LIV)? Or his unique way of defining the eyes, "the most precious part of the body and the one that distinguishes life from death by the use it makes of daylight"(XI, LII)?
How can this miniature ancestor of Kafka be forgotten: "It is surprising that elephants can even climb up ropes, but especially that they can come down them again, at all events when they are stretched at a slope. Mucianus, who was three times consul, states that one elephant actually learnt the shapes of the Greek letters, and used to write out in words of that language: 'I myself wrote this and dedicated these spoils won from the Celts'"(VIII, III)? (Note: all quotations are from the Loeb's edition).
Other reviewer compared the Natural History with the Guinness Book of Records. He probably took a minute off to write the review and then jumped right back to reading his number of People magazine. The Guinness is a compilation of isolated (and insipid) facts. Pliny's is an organic work, as Shakespeare's crowded plays or Montaigne's essays are organic.
Like any great work in human history -from Plato to Galileo, from Dante to Stephen Hawkings- Pliny's Natural History is, first of all, a work of imagination.