Originally Posted by invisible

There are multiple facilities at the top (L57) of MBS. Some are accessible by non-hotel guests, some - are not.

Pool (on top) and lounge (at L55) overlooking Marina Bay: accessible only to hotel guests, each guest needs separate hotel key to enter.

Observation deck : accessible by public, $23 per entry. You pay before going up and scan ticket's barcode at the gate.

Bars/dining: there are three, one at each tower. Ce La Vi at Tower 3, Spargo at Tower 2 and LAVO at Tower 1.
Ce La Vi requires that you pay $20 per person in terms of vouchers just to go up which then you can use for (obviously very overpriced) drinks and food. However, their fries are surprisingly good. There is a bar and restaurant. Views are on both sides.
Spargo does not have access at view on Marina Bay side, it is blocked by pool, but view towards south to Gardens is available. Also for Spargo you do not need to pay first to go to top.
LAVO up to recently did not require you to pay upfront before going, views are on both sides, but pretty much as soon as you get out from the elevator, they stick drinks menu in your hand and expecting to make order. You can politely ask them to show which seats/tables are available and once you select your place, you can/must order at something from menu.

Both for LAVO and Ce La Vi best time to go up to have a chance to find a table overlooking the bay is around 5PM-6PM and wait for sunset and see how color changes. If you go up after 8PM most likely it will be extremely noisy and busy.

Alternatively, these places give overview of Marina Bay from opposite side:

Lighthouse Bar at the top of Fullerton Hotel. No cover charge, can go up, take photos and if you feel it - stay and order a drink
Lantern at the top of Fullerton Bay hotel. The same - go up, walk around and decide of you want to stay and eat/drink something.
1-Altitude ($35/$45 entrance fee)
Zafferano (restaurant, no fixed cover charge)
And completely free access is at the top of National Gallery. It is further away but still gives quite good views of Marina Bay