Frankfurt is a literary city — Goethe's birthplace, the seat of the German publishing industry (the Frankfurt Book Fair every October is the largest in the world), and the host of the Adorno seminars at Goethe University. Some of the best books to read on a visit:
The Sorrows of Young Werther by Johann Wolfgang von Goethe. The 1774 epistolary novel that made Goethe famous across Europe and gave Frankfurt its first international literary celebrity. The hero's despair and suicide started a Europe-wide fashion (and a string of copycat suicides) and remains a remarkably modern study of romantic self-destruction.
The Frankfurt Trilogy by Friedrich Stoltze. The classic 19th-century Frankfurt dialect poet, whose comic apple-wine verses ("Hier draussen in der Schweiz...") are still recited in Sachsenhausen taverns and have given the city much of its self-image.
Minima Moralia by Theodor Adorno. Adorno wrote his fragmentary masterpiece of post-war critical theory in exile in Los Angeles, but he returned to Frankfurt in 1949 and ran the Institute for Social Research from a building on Senckenberganlage that still houses the descendants of the Frankfurt School. Difficult, brilliant, and the intellectual key to post-war German intellectual life.
Tauben im Gras by Wolfgang Koeppen. A 1951 novel set in a single day in Munich but unmistakeably about the spiritual condition of West Germany after the war — Koeppen lived in Frankfurt from 1947 and the book's themes of American occupation, displaced persons and uncertain rebuilding apply directly to the Frankfurt of the immediate post-war years.
The Tin Drum by Günter Grass. Not Frankfurt, but inseparable from the Frankfurt Book Fair where it was launched in 1959 — the first great post-war German novel and a permanent fixture of any Frankfurt literary visit.