Wherever there are hills in Thailand, you'll find monkeys, and there are two main hills in Phetchaburi. Firstly, they hand out in the car park and along the path to the Khao Luang Cave which is about 5km north of the town centre. Try and grab a stick or something for security if you come here. Another popular place where they hang out is along the road near the City Pillar at the northern end of the hill known as Khao Wang. I took the southern path down to the Wat Phra Phuttaya Saiyat at the southern foot of this hill and didn't come across any so they obviously hang out wherever there's more people.
There are large groups of Monkeys at the road up to the Cave.
As everywhere else if you meet them, try to keep your distance. - you donn't want to waste your time in some hospitals getting rabies shots because you have been bitten.
These here were very used to people - due to the many visitors - and tried to get some food from us.
Actually I am glad we had none, they lost interest soon. On the other hand I have seen people being chased around because they gave them food.
Also take care of your belongings. A camera or sunglasses are easy catch for them. And getting these items back ... not so easy.
Near the entrace to the Khao Wang Park, there are numerous monkeys that have a penchant for snatching things...especially food. If you've bought something to eat from the vendors at the foot of the hill, try to put them into your bag as these monkeys have a keen sense of smell and you can tell that when they're sneaking up to you.. Avoid disturbing the large alpha males as they tend to be territorial and aggressive.
If you're out an about in Phetchaburi after dark and on foot, and there's not so many people around - avoid the dogs and/or take a walking stick to wave at them. Because they are complete [moderator deleted] and you will get charged up to 5000 Baht for the series of rabies injections.
As you may have understood reading some other of my travel pages, I don't have a good relation with monkeys.
There are many of them along the path going up to the Khao Wang, especially close to the souvenir stalls.
They look healthy, well fed (even a bit fat, I would say), and quiet but, based on my personal experience, they may be annoying or even dangerous sometimes.