About 18km northeast of Senaki (half an hour by bus towards Martvili) are the ruins of Nokalakevi, capital of Egrisi (Lazica) from the 4th to 8th century. In AD542-555 Shah Khusro I (and his famous general Mermeroes and his elephants) failed to capture the city; but in 737 it was destroyed by the Arabs and remained in ruins until the first excavations in the 1930s by the German Alfons Maria Schneider, continued since 1973 by the National Museum, with the help of Cambridge University since 2001. Known to the Greeks as Archaeopolis (Old City), it's also been known as Tsikhegoji and Dzicha (Tsikhe and Dzicha meaning castle' in Georgian and Mingrelian respectively).
On a hill to the left a few kilometres north of Senaki you'll see the ruins of Shkhepi (part of a chain of signal posts from the Black Sea, and a pleasant jaunt) and continue on a reasonable road through two villages, before reaching a museum and the gates of the ancient city to the left immediately after the bridge over the Tekhuri River. The archaeological site has now been fenced and there will probably be a fee of a couple of lari. In the museum (10.00-16.00 except Mon), the first room on the left upstairs displays relics from the 8th to 1st century вс, including ritual clay animals, silver and bronze bracelets (there were gold ones too, now in Tbilisi) and Greek ceramics, attesting to trade links across the Black Sea; to the right are pithoi (funerary urns) from the 4th to 1st century вс, and replica coins, agricultural implements, weapons (sling and catapult stones, and arrow- and spearheads), and pipes from a 'calorifer' (underfloor steam heating), as well as a few ceramic pieces from the 6th to 18th century AD.
The ruins are entered by a right-angled trap area and a gateway through a massive triple wall; the outer wall, of big blocks, was built in the 6th century AD, and the next two, of smaller stones, date from the 5th and 4th centuries. The walls enclose an area of 20ha including a 4th/5th-century citadel and two churches on the mountain behind. There are also a couple of modern houses, with beehives, inside the walls; you'll also see a gatehouse with external stairs and the Church of the 40 Martyrs of Cappadocia (with tatty remains of frescoes, mostly hidden by a new iconostasis), both from the 6th century. Next to the church are the ruins of a tiny palace and the foundations of an older basilica, with those of a third church just to the west.
Beyond a house a tiny path leads up to a fort on a hill (as opposed to the citadel, higher up and reached by a jeep track to the north, a pleasant walk of an hour or so each way); at the northern end of a very solid 19th-century girder bridge (for pedestrians and bikes only) across the river are the remains of a 5th-century bathhouse (with three rooms for three different temperatures, and red ceramic heating elements). As in most Georgian forts, there's a tunnel down to the river, to get water during a siege. On the far side of the river is a popular, if stony, beach, and a road leading up into a dramatic gorge with popular hot springs a kilometre or two along. It's possible to stay at the archaeological base if it's not full.