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I would also like to know if there are any activities going on in Kuwait on weekends as i have a long weekend this time.

Rather than beating around the bush, I'll just say that Kuwait International Airport is the place to go for the weekend.

Explore malls..
Walk from the scientific centre to Marina Crescent, Salmiya..
Have some tea in Mubarakiya and take some pictures of older sellers, maybe buy an antique..
Try a new restaurant, there's a new one every month ..
Drive through Gulf road and put on some nice music..
You will need some nice company for all of the above.

you can visit the cinemas, a movie cost 3, or visit the beach, there are private beaches around and just a token is payed at the entrance.......There are also public ones also.  But generally you will enjoy Kuwait if you tag along with a friend to fun spots with a friend.

Mingle with locals, discver the full underground world and check internet for the cultural activitie, i.e. in 2:48 AM website 

Are there any °µÍø½ûÇø unions ? Maybe activities?

there many things that I like to do on weekends.. depending on the weather ..

i once walked from kuwait parliament sea shore at maliya /  kuwait city up till scientific centre in salmiya in month of march on a friday morning.

I like going for early morning breakfast at McD on gulf road opposite shaab garden

Things i've found so far.
Jet ski's seem to very cheap and good fun here. 25kd for an hour. loved it.
Smoking shisha.
There is paintballing, but i haven't tried it yet.
Malls... More Malls. That mall that's next to the other 5 malls.
Cycling along the seafront in salmiya. don't do it anywhere else, you will die.
Heading out in the Desert with friends (maybe).
The old souk in kuwait center is worth a wander around.
Hotel Spa/gyms have alot of °µÍø½ûÇøs in them.
Visit a few of the other gyms and count how many guys have glazed angry wide pupils.