Backtracking along the Pokhara Kathmandu road is the only sensible way to head down to the Chitwan National Park save taking a plane and even that is problematic.
Getting aboard a half decent bus is the first priority, most guesthouses will sort that out for you and take the strain out of the chaos at the bus park. Aside from Greenline there are no “luxury” buses heading this way so nearly everyone is in the same boat, or rather bus. I recommend a seat by the window in the middle of the bus, the front can get busy and in the back you will feel every pothole…and there are many!
The road climbs slowly out of Pokhara and begins its journey eastward to the mountains, the plains disappear and the gorges commence. Rapids run to one side of the road with adventurous white water rafters braving the rocks whilst stoic bus passengers cling, white knuckled, to their armrests enjoying the magnificent views; mentally drafting their last will and testaments.