Start your journey from Katihar to Bhagalpur early in the morning. After reaching Bhagalpur, visit the Pahari Mandir which is situated on top of a hill with a breathtaking view of the city. Spend a serene afternoon in the temple complex and enjoy the peace it offers. The temple is open from 6:00am to 6:00pm from Monday to Saturday and on Sunday from 5:00am to 7:30pm. Post that, travel to Ranchi, which is a 4-hour drive from Pahari Mandir. Spend the night in Ranchi.
After breakfast, head out to visit the Hundru Falls, a 98 feet high waterfall located on the Subarnarekha River. It is best visited in the monsoon season (June to September) to witness the falls in their full glory. After that, visit the Jayanti Sarovar, a scenic lake located in the center of the city. Finally, head to the Birsa Zoological Park and Wildlife Sanctuary for a glimpse of the local flora and fauna. The sanctuary is open from 9:00am to 5:00pm on all days except Monday. Spend the night in Ranchi.
Start your day with a visit to the Jubilee Park, a beautiful park in the heart of the city. Next, travel to Bokaro Steel City and visit the Bokaro Steel City Park. Spend some time here exploring the park’s beautiful flora and fauna. After that, head to Darjeeling via the scenic route. Check into your hotel and explore Chowrasta for some souvenir shopping and food. End your day with a visit to the Himalayan Mountaineering Institute which exhibits equipment used by Tenzing Norgay and Sir Edmund Hillary during their Mt. Everest expedition. The institute is open from 9:00am to 5:00pm on all days except Thursday.
If you have more than 3 days, take a day trip to Dhanbad to enjoy the beautiful scenic route. If you have less than 3 days, skip Bokaro Steel City and spend some more time in Ranchi and enjoy the city's local cuisines and rich cultural heritage.