Terracina's beach runs south from the town along the Riviera di Ulisse — a long arc of sand that stretches toward the Circeo headland. The beach is clean and pleasant, divided between free public stretches and stabilimenti balneari (private lido operations) that rent umbrellas and sunbeds. The private lidos are well-run and include showers and beach bars; the free sections are more basic but perfectly usable.
The beach gets busy with Roman day-trippers in July and August. If you want more space, head further south toward Fondi or north toward San Felice Circeo, where the crowds thin out. The water is clear and the Tyrrhenian is calm most of the summer — good for swimming and paddling.