1. Trekking Munnar is a real paradise for nature lovers and it's a perfect place to do many trekking tours! I personally fell in love with the bright green tea plantations. I strongly suggest that you explore the area close to Lakshmi Hills. In fact, you can walk nearly 10 km reaching an elevation of 1472m all while enjoying the view of Anamudi's peak, the highest mountain in the South of India. Along the path you'll have the chance to see tea and spices plantations (pepper, cardamom, cinnamon, cocoa, nutmeg...) and meet the tea workers.
Augustine (+91 9497678473) is a super nice guy who works as a guide in Munnar area and can organize among other things, amazing trekking tours, overnight camping, and jeep excursions! Feel free to drop my name if you decide to contact him :-)
There are a couple of scenic waterfalls in the area. My favorite is located at Athirappally, on the way from Kochi to Munnar. In order to reach this specific spot, you’ll have to leave your car in the parking area, pay a small entrance fee, and then walk around 10 minutes.
3. Tea museum and shopping
Even though I highly recommend you to sleep in one of the hotels/tents/resorts outside Munnar, I think that the main village is certainly worthy of visiting, even for just a few hours. Some of the main attractions include, visiting the tea museum, buying some spices and tea in the adjacent shop, treating yourself to some typical handcrafted chocolate, purchasing a saree to really plunge into Indian culture. Generally, most shops in this area will sell two types of sarees, the traditional Kerala style that is white with embroideries or the classic pan-indian style (many colors either silk or cotton).
4. Ayurvedic treatment or Abhyangam massage
After a long and intense day, pamper yourself with a (deep tissue) massage or Ayurvedic treatment! The Fog Resort has a nice SPA which offers many treatments that suite every kind of need! What I've found super interesting is the Shirodhara, also known as the "brain massage", done pouring hot oil drops on the forehead...you can’t miss it.