Erfurt --(15 min regional train)--> Weimar --(15 min regional train)--> Erfurt
Legs that spent the previous morning fighting red lights along the river Gera do not need a long journey the next day, and Weimar barely asks for one. The regional train from Erfurt Hauptbahnhof takes around a quarter of an hour, frequent enough through the day that there is no need to plan around a single departure, and the walk from Weimar's own station into the old town is short and flat.
September in Weimar tends to be mild and settled more often than not, closer to the kind of soft, late-summer light that makes an outdoor stroll comfortable rather than a chore, though a light layer for the morning train is still worth packing. This is deliberately framed as a recovery day rather than a sightseeing marathon of its own: the goal is easy walking, food, and a change of scenery, not another test of stamina.
The town itself rewards low-effort wandering. Weimar's old town is small enough to cover on foot without much strain, its streets mostly flat and its main squares close together, which matters more than usual the day after 26-odd miles. The Park an der Ilm, a long riverside green space running along the Ilm river at the edge of the old town, is the standout recovery-friendly option: broad, largely flat gravel and paved paths with occasional gentle slopes, shaded by mature trees, and long enough to make a short loop or a longer amble depending on how the legs feel. Benches appear regularly along the paths, which is worth knowing if the plan is to sit rather than walk for stretches of the visit.
Weimar's historic associations with Goethe and Schiller run through the town's museums and house-museums, several of which sit within a few minutes' walk of each other in the old town core. Entry prices vary by site and by season, so check current admission and any combined-ticket options locally before planning a full day around several of them; a single museum visit paired with time in the park is a realistic, unhurried plan for a recovery day. Weimar's market square and the streets around it also offer a good spread of cafes and bakeries for a slow lunch, a good fit for a body that has just finished a long training block and does not want to rush a meal.
For anyone who prefers to sit rather than walk for most of the day, the market square itself is a reasonable base: cafes with outdoor seating cluster around it, and people-watching from a chair counts as a legitimate recovery-day activity.
The walk from Weimar's station down into the old town is itself gentle, mostly downhill and along quiet streets rather than a busy main road, which makes it a reasonable first test of how the legs are holding up before committing to a longer loop through the Park an der Ilm. A regional day ticket covering travel within Thuringia can often work out cheaper than buying two single fares for the return trip, so it is worth asking at the ticket machine or checking current fare options before departure rather than defaulting to individual tickets out of habit.
Runners who want a change from museums entirely could spend the whole visit outdoors instead: a slow circuit of the park, a bench beside the Ilm to watch the water for a while, and a coffee back in the old town before the train home. There is no requirement to see everything Weimar offers in a single day, and for a body still recovering from 26 miles the day before, doing less rather than more is the better instinct to follow.
Getting home: Weimar is a day trip. Return to Erfurt by the same regional train line, generally running often enough through the afternoon and early evening that there is no need to book in advance, and confirm the current timetable before travelling since regional services can vary by day of the week.