His most famous book is In geheimer Mission durch die Wüste Gobi (part one in English Big Tiger and Compass Mountain), published in 1950.
There, Mühlenweg began to work as an accountant for Deutsche Luft Hansa, a newly formed airline company.
In 1927, Luft Hansa contributed to the Sino-Swedish expedition to Central and South Asia, following plans for an airline connection between Berlin and Beijing.
In 1931, Mühlenweg took his last and longest trip to the area, to observe weather conditions with a German meteorologist in the Gobi Desert.
His greatest success, In geheimer Mission durch die Wüste Gobi, was published in 1950 as the two parts Großer-Tiger und Kompaß-Berg and Null Uhr fünf in Urumtschi.