History's Still a Mystery. History's a Mystery series, #3

Matt, Ben, Nicky and Kris are four friends living in the small town of Coolongawong in New South Wales. They have spent the last two years in Mr Mac's classroom where they discovered that they could have magical adventures back in time by tripping on a creaky floorboard and saying the magic words, discovering history as it was being made in exciting, and sometimes dangerous, adventures. They must now leave the magic classroom behind as they begin high school in Orange.
Matt decides to invite his younger sister Olivia along on an adventure to the Klondike Gold Rush in Alaska. This, in turn, leads to her introducing her friends Grace, Will and Jack to the magic. Together, these four meet famous heroes, are present at some of history's most crucial times and visit many new places together. They discover the Warsaw Ghetto, China's Terracotta Army and the Great Wall, the airship Hindenburg, the Incas, the Taj Mahal and Stonehenge, with many other people and places in between.
Mr Mac's love of teaching history provides some of the destinations the four friends choose to visit. Others are the choice of the children.