Phra Bowon Ratchawang Si Tha

Phra Bowon Ratchawang Si Tha is what’s left of a royal retreat built in the 1850s-60s by King Pinklao, the Second King under Rama IV, on the west bank of the Pa Sak River at Ban Si Tha in Kaeng Khoi district. Almost nothing still stands — the roughly 150-rai site is mostly scattered brick foundations today, and much of the original grounds has been reclaimed as local farmland. There’s no entry fee, but also no ticket office, marked trail, or set opening hours, since no agency actively manages it as a visitor site.

King Mongkut sent his half-brother Pinklao to build the retreat around the same period Mongkut was building Phra Narai Ratchaniwet in Lop Buri, and the two projects are often mentioned together as companion pieces from the same royal building period. What survives are the low, rounded brick plinths of former timber pavilions — some finished with a lotus-bud brick-and-plaster edge typical of the era — spread across a site roughly 20 by 40 metres at its densest cluster. A stone landing once marked where boats could pull up from the river; the steps have mostly crumbled away with time.

Insider Tip: This isn’t a signposted stop — ask locally in Ban Si Tha or Song Khon subdistrict for someone who knows the path in, rather than relying on a map pin. It’s the difference between finding the site and wandering a cornfield.

Watch out: Don’t expect a maintained ruin with interpretive panels. What’s here is genuinely a scattered archaeological site on farmed land, with corn planted around and over parts of the old foundations — come for the history, not for polished presentation.

Kaeng Khoi district has a couple of easier, better-signposted stops if you’re building out a day around this corner of Saraburi — Pha Sadet, a limestone cliff with views toward Khao Yai National Park, and Khao Phra Phutthabat Noi, a climbable hill with Buddha-footprint shrines and cave temples, are both in the same district and considerably easier to just turn up to.