There are six cabin categories over three decks, although there's very little difference between most of them.
Cabins have either a double bed or twins so do check the deck plan carefully, as these are indicated. You can push the twins together, which we did, but the reading lights are positioned on the wall to accommodate the twin configuration, not double, and don't quite fit -- I kept sitting up in bed and inadvertently leaning on one of the switches.
All cabins have the same decor, which is very pleasing: white louvre doors on the wardrobe, a dark blue carpet and a floor-to-ceiling window so big that it's essentially a wall of glass. The heavy gray drapes are a blessing; in January, when we sailed, it was still light at 11 p.m. and sunrise was before 4 a.m. The cabins would be quite stark if it weren't for some lovely nautical touches; a leather stool, a leather director's chair, a circular mirror with a wood-and-brass frame and a wooden vanity with metal studs, leather drawer handles and the draw insides lined with vintage-effect map prints. A wooden box on top holds two metal flasks, which are yours to keep; there are water stations all over the ship and no plastic bottles anywhere. The wardrobe has six deep shelves and only 10 coat hangers -- but the cruise is short and you won't need to store any ball gowns.
Bathrooms are compact, with a decent shower (sadly, with curtain rather than screen, which is a missed opportunity) and a tiny basin over a storage unit. The big heated towel rail was extremely useful for drying off damp gear, although there were only four hooks; a coat hook on the back of the main cabin door would be helpful. Shower gel, shampoo, conditioner and body lotion are provided, as well as a hair dryer.
There are two power points (although one of ours was under the bed as we'd pushed the beds together), taking European-style round pin plugs.
Cabin grades are as follows:
Category B: Three Category B cabins, 202, 203 and 204, are on Magallanes Deck (2) and are the furthest forward. They are slightly smaller than the 177-square-feet. A grades thanks to a slight curve in the wall.
Category A: The remainder of cabins on Magallanes Deck, forward and aft of reception, are 177-square-foot Category A cabins.
Category AA: All that differentiates these AA grade cabins from the grade below is their location, on the higher Tierra del Fuego Deck (3). Decor and size are the same.
Category AA Superior: Also on Deck 3, cabins 321 and 322 are larger, at 220 square feet, and can take a third bed, so are a good choice for families.
Category AAA: The most expensive cabins are on Cabo de Hornos Deck (4), graded AAA and AAA superior, but they're exactly the same as those one deck below, just in what is perceived as a better location. Again, the "superior" category, 421 and 422, are larger, 220 square feet, and can take an extra bed.
Ventus Australis does not have any cabins adapted for disabled users. There are no suites, either.