Warframe has 3 openworlds, The Plains of Eidolon, The Orb Vallis, and The Cambion Drift. They all of their own unique setting and different enemies.
The Plains of Eidolon is home to Cetus, an Ostron reclamation colony protected by The Unum, a living tower believed to be at the pinpoint of the universe. The Unum protects the Ostron from the Grineer that hunt during the day and the massive Sentient Eidolon that stalk the Plains at night.
The Plains of Eidolon has many things to do. Bounties, mining, fishing, conservation, and during the night cycle the Eidolon Hunts. The Eidolons are split up into 3 parts, the Teralyst, Gantulyst, and the Hydrolyst, each one being more powerful than the last.
Conservation on the Plains is quite simple. Track and tranq the animal. Sometimes they attack you but other than that they run away.
Mining is quite simple too. Aim your mining beam at the gem or ore until the bar reaches a certain point then release and you have a gem or ore.
Fishing on the other hand isn't as easy as conservation and mining. YOu have to have different types of spears for different kinds of fish. There's also bait needed to attract some fish and the timing for throwing the spear. Sometimes you can even catch a boot.
The Plains of Eidolon also introduced the archwing launcher which will be talked about on the next page.
The Orb Vallis is on Venus and is home to the inhabitants of Fortuna, a Solaris debt colony of cyborgs.
The Orb Vallis offers many of the same thins as the Plains but a bit reprised. Conservation was first introduced in this update mainly because the map size is the largest of the 3 at a whopping ~2 kilometers by ~2 kilometers wide. In conservation your position from the animal you're hunting because they will run away from you if youre up-wind of them. Mining and fishing have stayed just about the same except needed an electrified spear for fishing and that the way mining worked was changed in this update.
The Orb Vallis also introduced a few new enemies and a new vehicle. The vehicle is a K-drive which can be seen in the photo on the left. This will be talked about on the next page. The enmeies that were added were the Orb Mothers. The Orb Mothers are monstrous robots with 4 legs and a wide range of attack capability.
In the photo above is one of the two Orb Mothers, The Profit Taker, a Sentient and Corpus amalgam. The only way to defeat The Profit Taker and her counterpart, The Exploiter Orb, archguns are needed.
The smallest and weirdest of the openworlds so far is The Cambion Drift. Housed on one of Mars's moons, Deimos, it is taken over by The Infested. Its other inhabitants are the Entrati, the family that discovered the Void, the place between places as I call it, and the source of the warframes powers. The day cycles on The Cambion Drift are quite weird as it is based on the Wyrms on the horizon. Vome with her gentle watch and Fass with is spiteful anger. Vome is blue the sister to Fass and represents night and Fass is orange and the brother to Vome and represents day.
This openworld doesn't have any large bosses to fight but instead it has Isolation Vaults which you can break into and kill a necramech and gain rewards. Necramechs will be talked about on the next page.