Here's another project made possible by plastic canvas (check DIY media basket for pic)....
You know the silk plant/flower section of home improvement stores? Well, that is where you can find the silk ivy used in this project. You can get enough for several caves for less than ten bucks. They're the ones that have the wire inside of their stems so they are pliable.
Anyway, you just pull each individual vine out of the spike at the base. Snip off the exposed wires at the base of each vine. Then, you want to make a small hook in the end. Slip the hooked end of the vine into one of the holes of the plastic canvas in the side. Loop it over to the other side and either snip one of the holes and run the vine trough it or secure it with some fishing line. A dab or two of aquarium sealant really helps keeping things secure.
Heres a diagram of how you do the vine stems on a canopy fashion. I omitted the leave to avoid confusion:
Once you have it constructed, clear a place for it to sit in the tank. Swish gravel to the side so the plastic canvas bottom sits nicely on the glass bottom. Then, pour some gravel over it so that the gravel falls through the leaves and onto the plastic canvas base. This will keep the cave stationary.
If you have a bare-bottomed tank, you can still easily construct this hide/cave. Instead of using plastic canvas, use a piece of plexiglass, you only need to figure a way to weigh it down. Firstly, use a file or sandpaper to sand the top edge of the plexiglass to remove the sharp edge. Next, you can use superglue to "tack" the vine into place. Then the aquarium sealant is used to make the final seal/connection. I suggest making a small loop in the ends of the section of vines so that the aquarium sealant has something to hold onto. Glue river rocks, gravel or whatever to the plexi-glass wherever you like. OR You can cut the plexiglass a little larger than what you intend the cave to be and glue the stuff to the flaps of plexiglass on the outside of it. Again, the possibilities are endless.
Heres a few pics of the plastic canvas way:
In the last pic, you see the intended recipient thoroughly enjoying the the safety that such a cave provides. Hes a big ol pleco that outgrew all of his other hidey caves.
Remember, if you have fancy goldfish in the tank this would go in, then be WELL and SURE to make the loops large enough so that no fancies can get trapped under them.