Kathisma is one of Lefkada's big west-coast beaches, a long sweep of pale sand and blue Ionian water backed by steep hills. It is popular and can feel crowded in high season, but its size means you can usually find space if you keep walking.
There are beach bars, sunbeds, and paragliding operators nearby, so it is not a wild escape. Watch the wind and surf before swimming; on rough days the same open coast that makes Kathisma beautiful can make the water demanding.