Phetchaburi is a very cool little town only about 2 hours by bus from Bangkok. You can take a van heading to Hua Hin from Ekkamai bus station and ask to be let off at Petcharat Hospital which is on the main highway. We’ve been there twice now, staying at the White Monkey guest house in the old town, which has modern ensuite rooms for only 500 baht. I could recommend you hire the very personable local guide Buppha Konglua who goes by her nickname Oh. First time last year we got her mainly for a one-day foodie tour. She hired a car for us and took us to the best eatery to try khao chae, a local specialty of jasmine infused rice in ice water, She then showed us a little factory where a kind of Thai sweets are made, and then we wanted to see “Uncle Tanom sugar palm plantation” which is a popular attraction for Thai tourists. The palm plantation was especially beautiful and you can see how they make palm sugar, an important ingredient in Thai cuisine. After that, we had a long lunch at Palmyra Tanote Kitchen where the highlights were incredibly delicious sugar palm fruit curry with shrimp and spicy fern salad. The last two destinations were out of town — we needed the car. To conclude our day, Oh showed us where to take a van back to Bangkok which would drop us at Kampheng Phet on the BTS and MRT mass transit lines, rather than Southern Bus Terminal which is way out of town.
Second time, this year, Oh took us to a reservoir where there is a big lake with a number of islands that have swimming monkeys. She bought a big bag of bananas to feed the little critters, some of whom came right onto our boat. Later we visited a place where sea salt is harvested. Oh also takes visitors into Kaeng Krachan National Park, the largest national park in Thailand consisting of rain forest on the eastern slope of the Tenasserim Mountain Range on the border with Myanmar. There you can hike and see many wild animal species and plant life.
Oh, Buppha Konglua, is on Facebook or you could PM me for her phone number.