City tour of Vientiane: the oldest temple Wat Sisaket (thousands of miniature Buddha statues), the former royal temple Wat Prakeo (once home to the Emerald Buddha), the sacred That Luang Stupa and the Patuxai Monument (Vientiane's Arc de Triomphe).
13:50 transfer to the train station (13 km, ~25 min). 15:30 depart by high-speed train to Luang Prabang, arriving 18:05 and transfer to hotel. Overnight in Luang Prabang.
B2B tip: Laos-China Railway tickets are tight in peak season and sold close to departure; book early. Passport required at the station. Allow the 1-hour check-in buffer.