The catchphrase for the Camden Beach at the roundhouse is 'you got 99 problems but the beach ain't one'. Well, actually, the truth is Camden Beach does have a problem; it's a victim of its own popularity. With the Camden Beach, you do get sand, deck chairs, rum based cocktails (eg ginger gay boy), etc. However, unlike the true beach experience, there is more stress involved than necessary. When the sun comes out, the lines at the bar are massive. And that's if you get in. But this is London, where people are generally willing to wait in line for popular things. If you're planning to chill out on a deck chair, think again. On a cold Monday evening, all deck chairs were in use. On a warm London evening, it was as packed as the tube in rush hour. Not the beach experience most people are looking for.
On a more positive note, the Camden Beach does bring a different experience to the table. Also, entrance is free and the place is open until 11pm. There are also a couple of screens to catch the Olympics action. There is also a ping pong table in the inside section of the 'beach'. If you are hungry, there are several food items on offer.
It certainly ain't Bali but if you want to chill out on some sand in Camden and have a cocktail, then by all means check out the roundhouse. Just mind the (annoying) crowds, especially during the happy hours (5pm-7pm Monday-Friday). Note that the Camden Beach is open until end of August but is closed on 4,11, 12 and 14 August.