Phnom Penh is not a big city and you will not find big amusement park or big shopping mall, but what we can find is something more relax, more refreshing. Something like a boat trip down the river and thankfully this is not too difficult to arrange in this city.
Maybe you cannot expect anything too fancy but a nice boat to get you slowly along the river to enjoy the sunset view is for sure. You can try Crocodile Cruise as they have a nice small boat but also big enough for a family BBQ, for price go through their link.
You can also find something cheaper that the Crocodile Cruise (of course with a difference kind of boat) for $15 per hour and and extra $3 for them to provide us with ice and Charcoal and we got the whole boat to ourselves (4 of us that is but the boat can fit more). There are bigger size boat if you have more people.
Bring your own meat and plate and drinks as it will not provide, and just enjoy the view.
For more info:
Mekong Flower Tour Boat, Tel: 011 977 484/012 432 268
Paris Le Mekong, Tel: 016 700 249/012 298 918/016 869 447
Mekong Boat Angkor Tel: 012 879 300/012 207 789
Or you can go straight to the spot and walk along the river you will find several boat trip: