This dagoba (the largest at Mihintale) is thought to have been built to house relics of Mahinda. On the far side you'll find the original, smaller brick dagoba, one of the oldest in Sri Lanka and largely ignored by visitors. From here, there are views over the lakes and trees to Anuradhapura.
A small temple at the side of the dagoba has a reclining Buddha and Technicolor modern frescoes – donations are requested. A room at the side is a devale (a complex designed for worshipping a Hindu or local Sri Lankan deity) with statues of the gods Ganesh, Vishnu, Murugan (Skanda) and Saman.