Match the obstacle to the next task

What is blocking you?Next task
Metal bars or a metal fence barrierGet the Hammer; see the sewer pipe guide.
Webs on the prison approachHit the webs with a Torch.
A Small Key lockUse a Small Key, not the Hammer.
The Iron Key doorCast the Iron Key at the Big Smelter.
The Prison Door lockUse the Prison Key.
The first door's full-stomach conditionEat before trying the door again.

Metal bars need the Hammer

The progression tool is the Hammer, shown here in hand. Do not substitute the similarly named War Hammer just because both sound like heavy weapons.

If bars surround the Hammer area, use the pipe approach rather than trying to break those bars before you have reached the tool.

The player holds a short-handled Hammer with a broad head
The Hammer has a short handle and broad head. Pick the Hammer itself when returning to metal bars.
Watch the creator’s Hammer chapter

A web blocker is not another lock

At the prison approach, the Torch clears the webs while the Prison Key opens the door. Carrying the key does not remove the web in front of it.

Also check whether a barred-looking structure is a door with a named key prompt. Its appearance alone is not a reason to treat it as the Hammer's metal-bar task. The prison guide keeps the approach and lock separate.

A Torch beside webs across a narrow stone passage in front of a barred doorway
Carry a Torch for the webs on the prison approach. Clearing the web and unlocking the Prison Door are separate tasks.
Watch the prison approach in May gameplay

Do not extend these answers to roots, goo or rocks

Do not use the prison-web answer as a reason to attack roots, goo or rock piles with a Torch. Treat those as separate barriers, and do not assume a side route is open in the demo just because a wider crafting menu shows more tools.

At the Jaguar Door area, keep the puzzle separate from the neighboring Iron Key door. Follow the named key-and-tool task instead of spending materials on a guessed clearing method.

Sources