The Vessel is the ship in which the aliens first arrived millions of years ago. It is shaped like a torus with a small section of the ring missing, with a front facing cockpit and several similiar, hexagonal structures situated around the middle section. The torus structure is hollow and can be entered through the gap, and access to one of the hexagonal structures can be gained through it. There is also an intact lifepod situated around the ring, still sealed and with no beacon.
The ship arrived there from another solar system, and crashed into Dark Bramble. Three pods were launched from it, each holding many cryopods. One was mangled before it escaped, now adrift in the planet. It can be found by flying towards an orange light.
Locating The Vessel
Using the information discovered in the mangled pod, describing the source of the "corruption" (giant orange glowing things) as the ship. Find one of the "Veins" (they are attached to the vines), look at which direction the Corruption is moving, then go the opposite way. When the Vein ends, or you're blinded by fog, keep going straight and you will be teleported to around 100 metres from the Ship.
When you check the map when in the area of the vessel, the map shows you are in the sun. By attaching a probe to The Vessel, one is able to find it 23 kilometres from Dark Bramble, far from the sun.
Watch out for anglerfish. Seriously. There are none near the Vessel itself, but as soon as you leave, you can very easily be found and killed. it is rather hard to get away from the Vessel. Head in any direction and you will be back in Dark Bramble, but if you so much as go backwards, you shall find yourself back at the ship's location. Avoid all white lights, keep moving forwards, and you'll make it out.