Corniglia is small enough that you can walk every street in an afternoon. The highlights are the medieval Church of San Pietro halfway along Via Fieschi, the Belvedere di Santa Maria at the village's seaward end (one of the best views on the Italian coast), and the Largo Taragio — the village's compact main square. The two trails out of the village, north to Vernazza and south to Manarola along the Sentiero Azzurro, are part of the experience even if you only do an hour of either.
There are no real beaches: Guvano, the long cove below the cliffs to the north, is hard to reach, and the small rocky landing at the Marina is for swimmers happy to scramble. The pleasures of Corniglia are slower — a glass of Sciacchetrà on the terrace, a walk through the vineyards, the early evening light coming up the cliffs.