Soul Sand Valleys were originally added as part of the Nether Update (1.16). The terrain is almost completely lit by constant fire, high and long falls, soul sand that reduces your speed (can be counterfeit by using boots with the Soul Speed enchantment), and constant spawning of Ghasts and Skeletons, making it extremely dangerous to explore.
A Nether portal is made by creating a 4x5 (2x3 on the inside) or larger door frame out of obsidian and then lighting the inside of the frame on fire with flint and steel or a fire charge. The corners of the frame may be left out, using only 10 obsidian as opposed to the usual 14. When one stands inside the portal for the first time, it will create a portal in its equivalent area of the Nether. A loading screen will appear during the change of worlds.
A portal can be shut down if part of the obsidian frame or the portal block inside is removed (not including corners), or the portal itself gets caught in the radius of an explosion (including those caused by a Ghast's fireball).
When re-entering the Overworld, any distance covered in the Nether is multiplied by 8, effectively making the Nether a fast-travel zone that allows greater distances to be covered in a short amount of time in the Overworld.
One has to stay in a portal. If not, it will not teleport a player. To use them, a player has to stand still inside the purple haze. A recent update allowed Overworld mobs to go through portals and vice versa. Attempting to go through a portal while in a minecart or on a pig will result in a player needing to restart the game to continue because a player can see permanent purple swirls. The same effects happen in the very buggy Far Lands.
A useful way to save obsidian is to create a Nether portal with the ordinary 14 blocks, travel to the Nether, remove the corner bits, then travel back to the Overworld and remove the corners there too.
Mobs
Ghast ― A flying, jellyfish-like, 4-block-cubed-sized monster which shoots fireballs and emits its terrifying trademark whispers and screams.
Ghasts can be damaged by any conventional weapons, but they do not get hurt when on fire. A ghast can fly into lava falls or lava lakes, but even if they burn, they don't get damaged (As of the November 10th Update). The fireballs they shoot can be deflected back at them using a fist or any tool by hitting it just before impact, killing it instantly if it hits (shooting an arrow or using the fishing rod on the fireballs works too). They drop gunpowder and ghast tears. Ghast fireballs cannot destroy cobblestone. For this reason, many players like to use cobblestone as protection. But ghast fireballs can destroy Nether portals, so it's recommended to keep ghasts away from them.
Skeleton - a common hostilemob that shoots arrows and drops 0-2 bones, 0-2 arrows, armor (if equipped), and/or a bow (most likely used, however, there is a small chance a bow may be enchanted).
Skeletons can be one of the most difficult hostile mobs to combat. Because of their climatic abilities in accuracy and fire-rate, skeletons are difficult to combat from a short range, with their maximum range being from 16 blocks away. Skeletons are best taken out with a bow, a shield and, if available, a strong sword. Because skeletons drop arrows, it is suggested to use the bow in this situation. Additionally, skeletons can't shoot through vines, but a player can. Another way of attacking it is to quickly sprint at it and go inside it (skeletons are non-solid) constantly and hit it with a sword. When one is inside it, the skeleton can't hurt one with its arrows.
It's worth mentioning the zig-zag technique (moving side-to-side, avoiding the skeletons' arrows) using the Soul Speed enchanting on your favor; this speeds up your movement, allowing you to do extra damage in less time than without the enchantment.
Blocks
Soul Sand - A brown block. When walked on, it slows the movement speed of a player and mobs that walk across it and makes them sink slightly, as soul sand is only 7/8 the size of other blocks. It can be used to create minecart-only passageways and docks, as well as one-way doors. Its slowing effect is doubled if an Ice block is placed under it. Some pixel-souls can be seen on this block.
Soul Soil - A brown block similar to soul sand and is only found in the Soul Sand Valley biome. It does not slow down players nor mobs, and fire lit on it becomes blue soul fire.
Bone Block - A white block which can be media Nether Fossils, which can be commonly found throughout the biome. They may generate as one of four different variants of the skull or one of four different variants of the spine, and in the 1.16 - Nether Update in the soul sand valley’s that are in The Nether, Ribs and Ripcages can be found in fourteen different variants.
