No permanent human settlement inside. Other expeditions are rare.
Amended D-302 Not for want of trying: every faction that tried to keep an outpost inside has failed (§31). The only people who live in the Tower are rare hermits, stranded there.
Cartographers leave sparse chalk/charcoal/mineral-pigment marks: incomplete circles, intersecting lines, radial diagrams, dots and geometric route notation. Marks vary by hand and age. They are human and practical, not magical runes.