Today we achieved a feat that only a tiny handful of humans have ever achieved: We entered the Antarctic Circle. At 6 a.m., we crossed below 66°33.79, heading into the most southerly recesses of our little blue planet. As we adventured onward, we were met with graceful swirling snow petrels, Antarctic terns, and Wilson’s storm petrels fluttering along icy tidelines and around magnificent icebergs. Sunlight streamed across the surface of the ocean from behind imposing mountains, which lined the edge of the peninsula.

After watching the sun rise over our picturesque surroundings, we heard a series of lectures. There was a talk on the penguins of Antarctica that covered the incredible adaptations these hardly little birds need to live in the frigid cold. From barbed tongues to super-insulating feathers, penguins have an incredible arsenal of evolutionary weapons. Next, we heard a talk on the seals—fitting after a morning filled with crabeater seals, both in the water and hauled out on ice floes! Pack-ice seals such as crabeater, Weddell, and leopard seals have managed to do away with the need for land in order to complete their breeding cycle. No such luck for elephant or fur seals, which still require land in order to give birth, mate, and, in the case of elephant seals, undergo their catastrophic molt.

Finally, I discussed the different whale species that we were likely to encounter on our Antarctic adventure. This focused on the great whales of the Southern Ocean, from the rare blue whale (the largest animal to ever have lived, weighing in at up to 200 tons) to the numerous and playful humpback whales.

In the afternoon, we Zodiac cruised through the bay at Prospect Point, surrounded by the Fish Islands. We were lucky enough to encounter an incredible Adélie penguin colony with hundreds of birds. Many of the chicks and adults were in their molting stage and looking uncomfortable and disheveled, with patchy feathers in strange patterns. This colony was next to a much smaller but equally beautiful blue-eyed shag colony. The shags also had large and curious chicks at this late stage in the season. With our Zodiac engines off, we sat silently and tentatively, watching and waiting as shags paddled their way over to inspect us.

After a successful Zodiac cruise, it was time to jump into the frigid waters of the Southern Ocean! With a water temperature of below 32°F, the polar plunge often a short affair. Nervous but excited people queued up for their swim while others watched from the sidelines. After dinner, we headed out onto the bow to catch the most incredible Antarctic sunset. Deep reds, purples, and pinks stained the white hillsides; seals scurried across ice floes; and the ship made its way through great pans of sea ice. The perfect end to a wonderful day.