The Walking with Series:

These stories are action-adventure books involving time travel and myths and legends. In each book the main characters travel back in time and meet a different myth or legend. All the adventures take place in different time periods travelling back from the most recent in 1969 to the most distant in 600 BC.

The Third Millennium Series:

A trilogy of adventure books set a thousand years in the future. Each follow the fortunes of the main character in 3033, 3036 and 3039. The first story takes place on the Earth fast becoming absorbed by a new ice-age; the second takes place under the oceans and the ice and the third takes place in space. The series is better read in order but can be read individually.