Tendon-driven continuum robots offer increased dexterity and manipulability in comparison to conventional rigid link serial manipulators. Being able to conform to complex curves in 3D space, continuum robots are in particular useful for applications in restricted and hardly accessible environments. The workspace of a tendon-driven continuum robot depends on the number of sections, as well as the length of each section and its range of bending radii. Common tendon-driven robot designs have fixed section lengths such that deployment along a tortuous paths requires additional linear translation of the whole robot. In this paper, we propose a novel tendon-driven continuum robot with extensible sections. A telescoping backbone allows control of the section length during operation in addition to bending through tendon actuation. Thus, the arc length of a section can vary and the range of bending radii is enlarged. As a result, the novel robot design inherently allows for deployment along tortuous paths in a follow-the-leader fashion. We suggest the use of spacer disks equipped with permanent magnets with alternating pole orientation. The magnetic repulsion forces enable equidistant spacing of the disks at any lengths of a robot section. We prove the concepts of our novel design with experiments using a first prototype.