During a break from school, they undertake a journey in a rowboat on a "river of time" that flows through a mysterious cave, emerging on a strange, primeval landscape.

The plot is somewhat similar to that of the novel Plutonia (1915) by the Russian palaeontologist Vladimir Obruchev, in which a team of Russian explorers enter the Earth's crust via an Arctic portal (a huge depression in the Earth surface created many millions of years previously by the impact of a giant asteroid, into which prehistoric animals had entered), and follow a river that leads them through a sequence of past geological eras and associated animal life.

Some scenes in Cesta do pravěku recall Arthur Conan Doyle's 1912 novel The Lost World, with four male protagonists exploring a prehistoric world where they find evidence of native human habitation, are attacked by a group of enraged pterosaurs, witness a twilight fight between a carnivorous dinosaur and a herbivorous one, encounter a Stegosaurus up close, and see one of their members, Petr, nearly chased down by a Phorusrhacos.

Possibly for the sake of continuity, Zeman also used models or 2-D profiles when depicting extant species including bison, a python, flamingoes, vultures, various antelopes, giraffes, and a jaguar (which was briefly spliced with footage of a real animal in one of only three instances of live species footage).

The use of 2-D profiles and 3-D models animated by concealed means had the advantage of filming in real time without the need for labour-intensive stop-motion.

Such a philosophy was unusual at the time and was more typical of later TV productions that depicted prehistoric animals in an educational context (including the BBC's Walking with Dinosaurs and Walking with Beasts series) which became popular following the advent of computer-generated imagery that negated the need for time-consuming, highly skilled manual animation.

In 1966, another version of the film was released in the U.S. by William Cayton whose company had been marketing Russian animated cartoons and feature films from the 1940s and 1950s, especially those of the famous Soyuzmultfilm studios (well known titles included The Firebird, The Frog Prince, Beauty & the Beast, The Space Explorers, and The Twelve Months).

In his film Jurassic Park, we can also see a very similar scene where examining the sick dinosaur was intended to get protagonists as close as possible to the reptile.

In February 2020, The Criterion Collection included the film as part of their Three Fantastic Journeys by Karel Zeman box set.