Colombo to Ella - what is the best route and what should I stop to see along the way?

The answer depends on how much time you have, but I will give you the optimal route most travellers should take.

The recommended route: Colombo → Kandy → Ella (via Nanu Oya / Haputale)

Go via Kandy. Yes, it adds a day or two, but the train journey from Kandy (or Nanu Oya, near Nuwara Eliya) to Ella is among the most scenic rail journeys in the world, and taking the direct route to Ella by road or via Badulla misses it entirely.

Recommended breakdown:
- Colombo → Kandy: 3-4 hours by train or bus. Arrive in the afternoon, spend a night.
- Kandy → Nanu Oya or Haputale → Ella: take the morning train from Kandy. The section from Nanu Oya through Haputale to Demodara and Ella is extraordinary — the train passes through cloud forest, tea estates, and crosses the famous Nine Arches Bridge area. Book this train in advance (2nd class reserved or 1st class observation carriage). Journey time Kandy to Ella is about 6-7 hours.
- Break the journey at Nuwara Eliya (alight at Nanu Oya station, 8km away) for a night if you want to explore the hill country town, or push through to Ella.

What to see along the way:
- Kandy: Temple of the Tooth, Kandy Lake, the market
- Nuwara Eliya: colonial town, Victoria Park, tea estate visits, Gregory Lake
- Haputale: Lipton's Seat viewpoint (Dilmah tea estate territory — extraordinary morning mist view)
- The train itself: the key experience, especially the Demodara Loop (the train circles below itself through a tunnel)

Direct Colombo-Ella by road or bus: possible in one long day but you miss everything above. Only worthwhile if you are returning and have already seen the hill country.