The Rundetårn, or Round Tower, has no proper staircase. Instead a spiral ramp coils up its insides, gentle enough that a horse and cart once hauled books to the university library and instruments to the observatory. Hans Christian Andersen was so taken with the place that in The Tinder Box he gave a monstrous dog eyes "as big as the Round Tower," and in an 1827 poem imagined a poet waking at midnight to find the tower gone, an abyss beneath him.

Christian IV finished it in 1642 as part of the Trinitatis Complex: tower, church and library, serving both science and God. Its observatory marked the starting point for measuring Denmark, the country's own Greenwich.

VoiceMap's self-guided audio tours trace Andersen's footsteps to the library where he read as a boy, and reveal how Christian IV's astronomical ambitions, born of wartime navigation, gave Copenhagen its ramped tower.