GURPS Ice Age is a solid little supplement that adds a wealth of interesting material for a relatively obscure period of gaming.
Complete with a collection of new hominid races, equipment, natural creatures, and spells, there really is a lot of content packed here in a relatively small package.
Presented inside are three ways to play; A historical campaign, a fantasy campaign, and a slap-stick caveman campaign. All provide unique ways to game and to interface with the history within.
While the book's age means that lots of the information in the book has since been replaced or amended by advancing archeological techniques, it manages to hold up for the most part, and shows a surprising amount of research of veracity for its time.
A great little package for anyone interested in the time period, or just to try something way out of left field for their campaign.