The most impressive stretches of the ancient wall are outside the site, north of the village of Mavromati. As you pass through Mavromati, pick up a copy of the excellent site guide at the postcard shop next to the village spring (5€). Even at a distance, the sheer size of the wall, with its towers and gates, makes most visitors gasp. The Arcadian Gate is especially well preserved; the grooves cut into the marble pavement by ancient chariot wheels are clearly visible. As you drive back toward Mavromati, you'll pass more of the defense wall and the site museum, which keeps irregular hours. Admission is 2€.
The excavated ruins of Messene are signposted past the site museum (officially open Tues-Sun 8:30am-3pm; free at press time, but probably not by the time you visit, when 3€ may be charged). This is a vast, sprawling site with a partially restored theater, an impressive agora/forum (marketplace), and a Sanctuary of Asclepius so large that it was originally thought to be the entire agora (city center and marketplace). The partially excavated stadium, with many of its marble benches well preserved, lies along the dirt road beyond the Asklepeion. A walk through the entire site takes a minimum of several hours, but it's possible to see just the Asklepeion in an hour. Keep an ear cocked for the tuneful frogs that live in several wells and cisterns on the site.