Catherine Falls, a two-tier drop near Coonoor, is the most photogenic of the region's waterfalls but also the least accessible — the viewpoint requires a short, occasionally slippery walk down from the road, so proper footwear matters more here than almost anywhere else on a Nilgiri itinerary.
Elk Falls sits closer to Kotagiri and is an easier stop — a short walk from the parking area to a fenced viewpoint, making it the better choice if you're travelling with young children or elderly family members.
Monsoon season (June-September) is when both falls are at their most dramatic, but also their most dangerous — barricades exist for a reason, and we don't recommend crossing them for a photo. Post-monsoon, October through December, still gives you strong flow with far safer footing, which is why it's the window we build into most of our waterfall-inclusive packages.