Is there a train or a flight?

No. Nội Bài is the nearest airport, and the rest is road.

What about going back to Hanoi?

Use the same roads in reverse. Ask at your homestay for the current bus departure.

Ba Be is road only. Take a coach from My Dinh or a car to Bac Kan city, then a provincial road up to the lake. No train serves the park.

Photo: Adam Jones · CC BY-SA 2.0

Mode	Time	Notes
Bus	Check on arrival	Coaches on the Hanoi–Bac Kan and Hanoi–Cao Bang lines leave Bến xe Mỹ Đình and often pass the lake. A morning bus also runs from My Dinh to Chợ Đồn, with a van on to the lakeshore. Ask for the current departure and fare when you book.
Car	About 2–3 hours to Bac Kan city. The lake leg is Check on arrival.	The Hanoi–Thai Nguyen expressway and then National Highway 3 take about 2 hours to Bac Kan city, cars only. Old National Highway 3 takes about 3 hours and allows motorbikes. From the city it is about 60 to 70 km to the lake, on provincial road 256 or on road 257 via Chợ Đồn.

How far is Ba Be from Hanoi?: About 240 to 250 km.
Is there a train or a flight?: No. Nội Bài is the nearest airport, and the rest is road.
What about going back to Hanoi?: Use the same roads in reverse. Ask at your homestay for the current bus departure.