The Uva Halpewaththa Tea Factory, not far from Ella, runs very informative tours. After you've enriched yourself with knowledge, enrich your taste buds by trying a sample of the estate's different teas. There's also a small shop (7.30am to 5pm) selling leaves and tea-related paraphernalia. Tours take place throughout the day but tour frequency times vary slightly depending on the kind of tea being processed. To be safe, visit in the morning.
To get there catch a bus towards Bandarawela, get off at Kumbawela junction, and flag a bus going towards Badulla. Get off just after the 27km post, near the Halpe Temple. From here you have a very steep 2km walk to the factory. A three-wheeler from Ella will charge Rs 500 return.