Thailand forum

You'll have to go to Kanchanaburi in order to go to Sangkhlaburi , even if you're just passing through on the train en route to the Three Pagodas Pass (where you can get transport to Sangkhlaburi).

You can take the train or bus from Phitsanulok to Ayuthaya, then another bus to Suphanburi. From Suphanburi there are buses to Kanchanaburi. This is a slow, but quite scenic and off-the-track route.

There are slow buses and minivans from Kanchanaburi to Sangkhlaburi. The buses take about 5 hours or more. The minivans are crowded, but arrive a couple of hours sooner than the regular bus.

There are buses to Kanchanaburi from the Norther Bus Terminal in Bangkok (Morchit) if you want to go into the city and don't feel like heading to the Southern Bus Terminal, or to Thonburi Station where trains leave for Kanchanaburi and beyond.

Another, more time-consuming, way to get to Kanchanaburi would be to take the train into Bangkok, then another train to Nakhon Pathom, then bus, songthaew or taxi to Kanchanaburi.

The road to Sangkhlaburi from Kanchanaburi is gorgeous, as is the landscape around Sangkhlaburi.

Sangkhlaburi gets packed with Thai visitors on weekends and holidays. Try and get there on a weekday if you can.

Echo everything Tilapia said - for me, I think the easiest way would be to head back to Bangkok. From there, you can take a minivan from Victory Monument to Kanchanaburi and another minivan from there to Sangkhlaburi . This way is quicker than the buses and you can get from Bangkok to Sangkhlaburi in 6-7 hours. If you've got a long-ish trip back from Sukhothai/Phitsanulok first though, it might be worth overnighting in Bangkok.

Also agree with Tilapia on Sangkhlaburi being busy at times, I find less so on weekends but especially over public holidays, such as the current long weekend (it's Chulalongkorn Day on Tuesday). You'll struggle to get a room at these times if you've not booked ahead. As for places to stay, P Guest House is the firm favourite but I also strongly recommend Chuen Jai House, though it's a little further out than other options. Haiku Guesthouse, at the back of Graph Café, is one I'll be trying next time I'm there (which is often, it's my favourite spot in Thailand!)

Enjoy your trip

UPDATE

5am 7am and 9.30am THB256

from the Thai Transport Company (Government bus) website