The Evros Delta is the strongest nature excursion from Alexandroupolis. The visitor centre east of the city introduces a protected wetland of lagoons, reed beds, river channels, and migratory birds near the Turkish border.
Rules and access can change because of the border zone, so contact the centre before assuming you can roam freely. With the right timing, especially during migration periods, the delta is a serious birdwatching stop rather than just a scenic marsh.