Minecraft Speedrunning/Ruined Portal
Ruined Portals are a new structure added in 1.16 and can spawn in both the overworld and the nether, although the overworld ones are most useful. There are 13 different ruined portal variants, with different chest locations so learning them can be useful. The chest can contain useful loot such as a flint and steel or fire charge for lighting a nether portal, flint for crafting a flint and steel, gold or iron nuggets, obsidian, gold blocks or enchanted gold armour.
If the ruined portal contains no crying obsidian in the portal part of the structure and you have some obsidian in your inventory or in the chest, the portal can be completable meaning you just need to place the obsidian down and light the portal without the need of a bucket although this is somewhat rare
There can also be enough lava to build a nether portal using the normal bucket method to enter the nether.