Oplontis is a big word that refers to a special place that was very important a long time ago. It's an ancient Roman villa, which is like a really fancy house where rich people used to live.
The villa was found near a town called Pompeii, which was destroyed by a big volcano a long time ago. Some smart people decided to dig up the villa and figure out what life was like for those rich people back then.
Now people can visit Oplontis and see what the villa looked like a long, long time ago. They can see beautiful artwork and fancy rooms and furniture. It's like taking a step back in time and seeing how people used to live a long time ago.