Self-closing gates.

[serVar161]

Gates that close automatically using mechanisms or counterweights.

Option 1. Single.
After the gate is opened, it closes automatically after a while under the force of gravity acting on the counterweights.
Implementation:
"Corner post with mechanism." To build self-closing gates, "corner posts with mechanism" are used instead of corner posts. When preparing a gate with such a post, a second corner post with a mechanism is installed, and the gate built between them will automatically close after a certain time.

Option 2. A set of two gates.
Two gates are connected by a chain or rope through pulleys. Initially, one gate is open, the other closed. The mechanism and the length of the rope/chain are designed so that when one gate opens, the rope/chain tightens and pulls the other gate through the pulleys, closing it. Because of the pulleys, the direction in which the gates open is irrelevant.
Implementation:
A chain wall is built from corner posts with a mechanism from one gate to the other, forming a closed chain with two gates. Gates connected in this way will open and close alternately. When one gate opens, the other closes.

Option 3: A portcullis.
A system of two bars that raise and lower. A counterweight system is designed so that when one bar rises, the other lowers.
Implementation:
Instead of building a gate, propose building a portcullis. If the corner post is a standard one, it is raised and lowered manually. If the post is equipped with a mechanism, the same principle applies as options 1 and 2. If not connected to another gate or bar, the automatic gate closes after a certain amount of time. If connected to a closed chain, it rises or falls depending on the state of the object to which it is connected.

[Frogg]

And you need a spring from the cash shop to build it. Never before seen.

[Regulus2424]

Spring? Nah mate, it's gonna be a little magical fairy

[serVar161]

And you need a spring from the cash shop to build it. Never before seen.

A spring? For what?
You might be picturing modern door closers. And despite the fact that "spiral springs for mechanisms were invented in the early 15th century," these mechanisms use simple pulleys (3rd century BC) and counterweights (around the same time).

[magnet]

every time he posts, he gets stronger. we have to find a way to stop him before it's too late

[serVar161]

every time he posts, he gets stronger. we have to find a way to stop him before it's too late

It's late.

What do you think about the gates?
They're actually quite simple. The mechanism is much simpler than a mill.

Imagine you drive a cart through the gates, and they close automatically behind you. No need to go around the cart.
No need to worry about whether you've closed the gates or not.
Same with the double gates. An automatic "airlock." Into the same mine.

And no magic or modern technology involved—just ordinary medieval mechanics.

[DoctorCookie]

When do you have time to play?

[Frogg]

I never understood the importance of self-closing doors. Do players often forget to close them?

[lordgrunt]

next stop: redstone circuitry

[serVar161]

When do you have time to play?

There's plenty of time. Of course, it's always short, but there are tasks that take a long time and don't require supervision. While chopping down trees, I wrote a couple of lines, assigned a task to harvest a flax field, and then another couple of lines, and there are plenty of other activities like that. You can think while doing anything.

Speaking of thinking, what do you think about automatic gates?