If you are in Jakarta over a weekend and don't want to spend it trailing around shopping malls, why not consider a short dive or snorkeling trip to the Thousand Islands (Pulau Seribu).

There are several tour operators who can arrange this trip. Prices will include the boat transfer from Ancol marina (fixed schedule) to one of the islands which has a hotel on it (e.g. Putri, Tiger). Food and accommodation are also included in the package. If you wish to dive or snorkelling, that would also be included.

Boats run on fixed schedule, few morning departures from the marina. The return trip will be either in the afternoon (around 2PM)or in the late afternoon (ie. 5PM)

The accommodation ranges from villa-on-stilts, regular wooden bungalows, to modern concrete cottage. 

The diving is nice, but not as spectacular as you will see in other places in Indonesia. It is also appropriate for all levels of qualification. Parts of reef are pretty broken and dead, but parts of it are really nice. You can see plenty of things, from crown of thorns, fire urchins, colourful sponges, box fish, clown fish, bat fish, etc. You wont really see shoals of fish though. Putri island also has an artificial reef which is teaming with fish and has plenty of coral growing on it. In some places you will find steady currents, but not particularly strong ones.

Some of the islands have interesting wildlife: monitor lizard ("biawak" in Indonesian), endemic birds are regular inhabitants on the land. There are few wildlife conservation area in certain island. 

Some of the islands also serve as historical site whereby one can find ruins of fort and other buildings from the colonial era. Some of them are Bidadari Island, Onrust Island, and Kelor Island. Only Bidadari Island is being developed to have accommodation while the other two were kept as is. 

The trips are quite expensive for what they offer in terms of luxury. However... if you are on a short trip to Jakarta, it could be the perfect way to relax over the weekend.