What's the large pipe on top of M/S Viking Grace?

What's the large pipe on top of M/S Viking Grace? - Mountain Covered by Snow

It looks really weird and I can't understand its purpose. Is it for making the vessel look better? An exhaust? Does anyone know what it it? Apparently it didn't have it in the beginning and it seems it's been moved after being put on the ship. It's rotating and it's glowing during night.

What is it?
Why was it moved?

ferries cruising baltic-sea viking-line

Pictures about "What's the large pipe on top of M/S Viking Grace?"

What's the large pipe on top of M/S Viking Grace? - Aerial Photography of Rocks Beside Body of Water

What's the large pipe on top of M/S Viking Grace? - Sailing Boat

What's the large pipe on top of M/S Viking Grace? - Rusted metal leaking pipe above grassy meadow

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Images: Tirachard Kumtanom, Luciann Photography, Luciann Photography, eberhard grossgasteiger