Phsar Reatrey goes from late afternoon until around midnight every Friday, Saturday, and Sunday. Although you may see foreigners and tourists there, mostly locals attend this market.
There are live music acts each night at various times, as well as roaming performances that pop up. It is located on Sisiwath Quay, near Riverside Park.
There are also market stalls that stretch all the way along the river up to the Royal Palace, which looks gorgeous with the overhanging lights along the road.
You can try lots of street food - including eels, tarantulas, crickets, and more. Surprisingly, the tarantulas taste delicious - and are worth a shot! These will accrue tourist prices (KHR4000/USD$1 for a tarantula, KHR6000/USD$1.50 for a snake, KHR5000/USD$1.25 for a squid, or KHR16000/USD$4 for a bag of mixed bugs.
For a more local dinner, join any of the tables along the riverside where you can get Num Banh Chok (Khmer rice noodles). Pick a table that has a lot of locals at it and sit down. A meal will only cost KHR5000 (USD$1.25). Bring cash, nowhere takes card.
For Phnom Penh, we lashed out and paid USD$34 for a nice hotel with traditional Khmer art. The rooms were massive, had aircon, balcony, bathtub, couch, large bed, and rooftop pool and bar.
We booked Okay Boutique Phnom Penh for our first and last nights and were able to store a bag here with them for the duration of our travels around Cambodia. I did have the breakfast one morning and it was expensive and overrated. Due to a booking error (this is why I never book in advance) they gave me a complimentary breakfast - but for USD$10-15pp you'd be better off going to any of the amazing cafes or street food nearby.
The central market is a great place to visit and buy your souvenirs, as well as try Balut, which is a fertilised duck egg.
There are touristy sections of the market, but most of the market is designed for locals. Make sure to barter your prices here.
This is the tallest buddhist temple in Phnom Penh and is a 14th century pagoda. Tickets only cost KHR4000 / USD$1.
This is a nice visit to do if you're walking around the city. You are likely to spend anywhere from 20 minutes to 2 hours there, but it's not the type of activity that will take you a whole day.
This one is a difficult visit, but a must-do while in Cambodia. Especially if you are at the start of your trip, it is very important to understand the background of what the Cambodian people lived through prior to exploring this beautiful country.
Choeung Ek was a designated site for mass executions. More than 20'000 prisoners from S-21 and other sites were executed at Choeung Ek. There are several mass graves and horrific sites at this place, but it is important to understand the history.
The Centre is very well looked after and upon arrival, you receive an audio head-set to undertake a self-paced tour as you walk through the grounds. It's not necessary to do the tour with a tour group, and I would actually advise against it. You will get more information doing the audio tour at your own pace. It's a very heavy pace, and visiting with a large tour group (in which people may be taking selfies or making ignorant jokes) can be really uncomfortable. You can get to Choeung Ek Genocidal Centre easily via tuktuk, which will cost around KHR 15'000 / USD$3.75 each way. Entrance and an audio guide is KHR 24'000 / USD$6 per person.