This adventure starts out a little simple. The players were part of a small trade caravan traveling through the lands. The idea is that they took this easy job for free travel and some food while they wait for their stop.

At some point, when the caravan parks for the night, you hear noises and a faint yell from a nearby cave.
Through the cave they pass some golbins and a man on the brink of death. Through coughing blood he hands you a small crystal. He tells you to go to his friends up ahead. He tells you he needs you.

You go through the small hole in the cave wall and find yourself in a grand hollowed out chamber. Rain falls from the sky and water rapidly runs below you. At the end of the stone bridge you find a group of 3 people. They raise their weapons for a moment but lower them as you approach calmly.
They explain to you that they are from a slightly different world. One of them is wounded and a woman in white and red robes is tending to him. They tell you about a peril hitting their world. The wind has topped, the earth is rotting, the ocean boils and extreme heat from volcanic mountains is scourging all around it. They urge you to take their crystals and walk through the nearby doorway.

You pass through and a moment of disorienting darkness hits you. You open your eyes to green fields and a grand castle town surrounded by trees which have seen better days.
As a side note, this campaign made in Roll20 also features music by Kevin Mcleod! A lot of it is basic 8-bitty tunes, but it adds a fun dimension!

I have used some audio at the table before! For another campaign, Clear Skies, I would throw rain sounds over generic "fantasy" town ambience. Having a track run with woodland noises add a fun layer to the tabletop experience!
For those who have played it, here is where the campaign truly start. It's Final Fantasy 1 retold! The whole world is imported in Roll20 and I have set a few encounters all over the place. While generally it follows the plot of FF1, players can always go off the rails a little if they want.

Some NPC's might talk about people they know going missing. While some may have fun similair portals, others simply lost their life trying to escape their dying surroundings. A background plot about the use of the portals is scattered here and there.
The heroes arrive in the town first and are greeted by land still mostly untouched by the worlds decay. It's residents still a little aloof about the dangers encroaching. They are directed to the castle. NPC's will remark how you look like a band of warriors strong enough to rescue the princess of Corneria.
The Castle itself has it's guards patrolling around and it's servants running their errands.
The players go to the top of the castle and speak to the king. He informs them about Garland, a knight who once fought for the kingdom but has changed over time. He has kidnapped the princess for an unknown purpose and the king is sending every one capable to get her back safely.

The king directs you to the north, to an old castle where Garland is holed up.