From Mumbai
You can catch the Kurla-Coimbatore Express (1013), leaving daily from Kurla station on the Central Railway in Mumbai.
From Bangalore
The Bangalore Kanyakumari Express (6526) leaves daily. For early risers, the Bangalore-Coimbatore Inter-City Express, another daily train, is a good bet.
From Chennai
The Chennai-Coimbatore-Kovai Express (2675) leaves daily.
Chennai-Mangalore West Coast Express (6627) also has a daily service. Chennai-Coimbatore Shatabdi Express (2023) leaves daily except on Wednesdays. This one's a chair car. Another daily is the Chennai-Mettupalayam Nilgiri Express (6605).
From Kochi
The Cochin-Guwahati Express (5623), which leaves on Tuesdays. A more frequent option is the Cochin Barauni Rapti Sagar Express (5011) which leaves every Tuesday, Thursday, Friday and Sunday.
Distance from Ooty to