When Twain arrived in Germany, his writer’s block had hamstrung not only “Huckleberry Finn” but also several other books, including “Life on the Mississippi” and “The Prince and the Pauper.” And he had humiliated himself in December 1877 with an irreverent speech in Boston before some of America’s greatest literary figures: Ralph Waldo Emerson, Henry Wadsworth Longfellow and Oliver Wendell Holmes. “I feel that my misfortune has injured me all over the country,” he wrote to a friend. He told his mother that he needed to “fly to some little corner of Europe.”

I arrived in Heidelberg in June with some sense of Twain’s restlessness. When I told a friend that I was having trouble concentrating, he said I should stay present: open my senses to whatever was happening at the moment, and exist in the world instead of in my head. As I reread “A Tramp Abroad,” knowing that Twain had arrived in Germany under a cloud of shame and failure, it seemed to me that he had faced a similar challenge. His goal was not so much to penetrate Heidelberg and the Neckar Valley but to soak his senses in those places, to dissolve his insecurity in the scenery and to rediscover his pride and purpose.

This comes through clearest in Twain’s Neckar narrative, so I followed him upriver. From Heidelberg, I took a boat to Neckarsteinach, an old town with a quartet of castle ruins. The river winds between hills like a lazy cursive signature. Time has worked slowly on its banks: The terrain is still mainly field and forest; the mountains robed in thick green foliage. Every few miles our boat passed a village with bored-looking teenagers and rows of simple white homes. After sundown, the buildings glowed like votive candles in the dark.

The inns where Twain stayed along the Neckar have closed, but some of his favorite castle ruins are now connected with hotels. Burg Hornberg is a mountaintop fortress surrounded by terraced vineyards, with a tower so high that surely, at some point, someone must have locked a princess in it. The hotel’s impressive view of the Neckar is marred only slightly by an industrial plant.

Farther downstream, you can stay at the Schlosshotel Hirschhorn, whose ruins were one of Twain’s favorite Neckar sights. “The clustered brown towers perched on the green hilltop, and the old battlemented stone wall, stretching up and over the grassy ridge and disappearing in the leafy sea beyond, make a picture whose grace and beauty entirely satisfy the eye,” he wrote in “A Tramp Abroad.”

Twain’s Neckar story is filled with these moments of sensory immersion. He luxuriates in the “green and fragrant banks,” the vineyards, the poppy fields. In these sensual descriptions, Twain’s language often turns therapeutic. The raft, he wrote, “soothes to sleep all nervous hurry and impatience; under its restful influence all the troubles and vexations and sorrows that harass the mind vanish away.” In Germany, Twain was finding the equilibrium that had deserted him at home.