To reach Wadi Darbat, you can fly into the Salalah International Airport. Wadi Darbat is a one hour drive away from the airport.
Many airlines can be taken to go from India to Muscat such as Oman Air, Jet Airways, IndiGo, Air India, SpiceJet and Air India Express. There are flights from Kerala (Kochi, Kozhikode and Thiruvanthapuram) that fly directly to Salalah. From Muscat to Salalah, there are regular Oman Air flights (3 daily).
The best way to reach Salalah is to fly from Muscat or Dubai. From Muscat, it is a 90 minute flight, and from Dubai it is a 2 hour flight. You can fly in with Oman Air.
From Muscat to Salalah, it is a long 12 hour drive. Wadi Darbat is a bit farther. It is a beautiful drive from Muscat as you will pass small towns and you could make stopovers at Nizwa. The first 5 hours on the road are pretty and super scenic while the rest of the trip gets boring as it will just be a long desert and some oil fields.
From nearby cities. Talk about connectivity, compare different services (if any)
There are daily buses between Omani cities as well as Dubai which are all operated by the Gulf Transport Company. This is relatively cheaper than the costs of flying or taking a cab.
From nearby cities.
You will need a car to reach Wadi Darbat as there is no other transport option.