Romaurie effect

Saw that's pond on the Internet that the person made a view for their fish where they could get out of the pond into a small square fish-tank and people could see the fishes that enter this transparent square box inside the pond.

Looking around I learn that some call it the Romaurie effect and that help a lot in the search for more answers on how it's done.

How it's done:
But a transparent glass or plastic.
See that all four sides are glued perfectly. Don't forget to glue it with aquarium glue.
Let it dry 24 hours.
Test the square put water and see if any water runs out.
When ready make 1 or 2 or 3 holes to the transparent box at the bottom so fish can enter. Don't do the holes at areas where it won't be under water.
Put it down into the aquarium.
Take a small tube as the air tube from your aquarium and blow out the air from the transparent box.
While air is leaving the box you must add more water to the aquarium.
Let the aquarium and box rest for 24 hours. Rest? Yeah, let it sit there with no fishes to see if it's done right and no water is leaving the upgraded aquarium.
Now let's add fishes..
How cool is it to see the fishes swim on the transparent box.

Remember always check your new upgrade to your aquarium once a day to check for holes where the glue is located.