ThunderClan

ThunderClan is one of five clans living in the forest. They are mainly known for their 'courage and loyalty' as said by Firestar in Secrets of the Clans

The information below is from the official Warriors Wiki

Description
ThunderClan is a mainly peaceful Clan, and respectful of the other Clans as well. In battle, ThunderClan is fierce, courageous, and loyal. They are known to often take loners and kittypets into their Clan to either swell their ranks or because the cat is in need of help or shelter, although this did not happen much until Firestar became leader of ThunderClan. For this, they are at times looked down upon by other Clans and thought of as weak. The Clan's main prey are mice, voles, squirrels, and the occasional rabbit, as well as birds such as starlings, magpies, wood pigeons, blackbirds, and thrushes. They have excellent stalking techniques, creeping across the forest floor. They have the sense to keep upwind of their prey in the thick bushes. ThunderClan cats are noted to be especially strong. They are the only Clan to bunch their hindquarters before leaping to catch their prey

Forest territories:
The ThunderClan forest territory is located in what Twolegs call the White Hart Woods. The territory also includes Twoleg places such as Windover Road and Chelford Forest. Landmarks in this territory include: The camp entrance is well hidden by brambles, which protect the camp from predators, but doesn't stop sunshine from coming in. A ravine leads through it. This ravine was once a river, but it is now dried up. The way into the camp is through the gorse tunnel. The nursery has thick bramble walls and is the most guarded part of the camp. Behind a tree stump, there is a clump of ferns where the apprentices sleep. Warriors sleep under a bush in another tunnel. Inside the camp, there is a fallen tree where the elders sleep, and the senior warriors sleep in the center of the camp. Across the clearing, a smooth tall rock resides. This is called the Highrock, the leader stands there to make important speeches. The leader's den is in a cave where the rock was carved out by an ancient stream. Lichen covers the entrance. The last notable feature in the camp is a fern tunnel that leads to a crack in a rock. This is the medicine cat's den.
 * Camp - It lies at the foot of a sandy ravine, protected by thornbushes. The camp is easy to defend and hard to attack. This is also where the Clan lives and mainly functions.
 * Tallpines and Treecut Place - Pines near Twolegplace. Usually filled with Twoleg tree-eaters, the ground there rumbles and leaves deep gullies filled with muddy water.
 * The Great Sycamore - One of the largest trees with strong and thick branches,
 * The Owl Tree - A tree that serves home to a tawny owl, apprentices here dare each other to climb its trunk
 * Sunningrocks - Rocks that absorb the sunshine and are a place of relaxation. Moons ago, it used to be an island belonging only to RiverClan, but when the river changed the current, ThunderClan wanted this territory, too.
 * Snakerocks - Home to venomous adders. The caves beneath the rocks can also be homes to other dangerous creatures.
 * The sandy hollow - A training hollow with soft sand so apprentices don't hurt themselves.
 * Twolegplace - The place where Twolegs live. This place is avoided at all costs, but useful catmint can be found here.

Lake territories
The lake territory for ThunderClan is called the Hare Hill Woods by Twolegs. Twoleg landmarks nearby include the Hareview Campsite, Abandoned Workman's House, Quarry Road, and the Quarry. Landmarks here include:
 * Camp - The camp is well protected by the side of a cliff, and surrounded by a thorn barrier.
 * Greenleaf Twolegplace - This part of land was given to ShadowClan until ThunderClan fought for it back.
 * An abandoned Twoleg nest - Herbs and prey thrive here, though it has an ominous feeling inside.
 * Sky Oak - An ancient oak where squirrels love to call home. It also has an old rabbit burrow inside. It‘s where ThunderClan apprentices practice their climbing skills.
 * Old Thunderpath - Marked with blue Twoleg markers, cats often stay away from this road.
 * The clearing - A training hollow much like the old sandy hollow in the forest territory.
 * Lake shore - ThunderClan has the north-eastern portion of the lake.
 * At the bottom of an old cliff, this camp is very well protected. The walls around the camp are smooth, indicating Twolegs cut this place moons ago. The cliffs also help keep out the wind. A thorn barrier guards the camp; any cat that wants to come in has to get past. A ledge peeks out from the cliff. That is the Highledge where the leader speaks. A cave near the top is the leader's den. The apprentice's den is also a cave in the rocks while the warrior den is under a big thornbush. The medicine cat's den is another cave, but this time hidden by bramble tendrils. Like the previous camp, the nursery is highly guarded, and under a big bramble thicket reinforced with thick roots woven together for protection. Lastly, the elder's den is in a hazel bush, and later rebuilt under the boughs of a beech tree and reinforced with honeysuckle.