Ian, Barbara and the Doctor endure the heat of the desert.
In the opening episodes of this vast adventure - which ranked 84th (of 241) in Doctor Who Magazine’s ‘First 50 Years’ poll of 2014 - the First Doctor, Susan, Ian and Barbara ran into the Venetian explorer Marco Polo, who transported them and their temporarily kaput TARDIS down from the freezing Pamir mountains. Marco, whose cross-Cathay caravan carries the Mongol warlord Tegana to a peace conference with Kublai Khan, means to present the Doctor’s TARDIS as a gift to the Khan, so he may leave his service. He’s con. scated the TARDIS key… but the crafty Doctor has made another.
Not all of the locations given in Marco’s journal entries throughout correspond to modern-day locales, but there’s enough information given to enable us to calculate (via Google Maps) how one would go by modern roads. So: from the eastern edge of the Pamir mountains to Lop County, around 355 miles; to Dunhuang, 956 miles; to Jiuquan, 246 miles; to Zhangye, 129 miles; to Lanzhou, 313 miles; to Yinchuan, 274 miles; to Shangdu County, 537 miles; then another 241 miles to Beijing, making an overall total of 3,079 miles. In the second episode, it’s implied that 20 miles a day is good average progress for the caravan… so the entire journey would seem to take place over . ve months, or thereabouts.