Ditch Plains is Montauk's classic surf beach. The break is friendly enough to attract longboarders and beginners but steady enough that local surfers take it seriously, especially outside the most crowded summer hours.
For non-surfers, it is still a good beach: broad sand, low bluffs, and a less polished feel than the beaches farther west in the Hamptons. Parking rules are strict in season, so check before assuming you can just roll up.