The major sight in
Veliko Tarnovo is the Tsarevets mediaeval fortress and you would never be forgiven if you came here without
visiting it.
There is more to see and do, however, than Tsarevets, including various mediaeval churches with well-preserved frescoes (if that is your thing), a couple of decent museums and the lovely cobbled streets of the old town with houses built into the rocks.
The Samovodska Charshia that starts near Tsarevets and leads to the town centre is lined with lovely little craft shops and cafes as well as a few local craftspeople demonstating copperwork, woodwork, weaving and traditional sweet making.