A small unmarked shop opposite the eastern entrance to the Nellaiappar Temple, Iruttu Kadai is the most famous halwa shop in Tamil Nadu. It opens only in the late afternoon, sells out within hours, and is the benchmark by which every other Tirunelveli halwa is measured.
The halwa itself is a dense block of refined wheat starch cooked for hours with sugar, ghee, and cardamom — translucent, glistening, and so rich it should really be eaten in small slices. Locals buy it by weight and take it home wrapped in greaseproof paper. Get there before 5 p.m., bring small notes, and don't expect a sign or a queueing system — it's all wonderfully chaotic.