Want to make a cave..

[Bloo]

Personally I prefer the natural sort of way i.e. strategically placing stone and slate, angled bogwood etc.
So in essence, the same as Inchworm. I've tried the pots, pipes etc. but I just prefer the natural way

 

[Kirsty]

I used a small terracotta pot which i have cut in half so i have two small places to hide.

Sebastian my crab has one and Tigger my catfish has the other.

 

[abstract]

i have used terracotta pots, pvc pipe coated in sand, driftwood, and slate....

my favorite method of the 4 is slate since it is extremly cheap and you can make literally ANY pattern/shape/size cave you want

my 2nd favorite is the pvc covered in sand (using silicone) ...in a properly aquascaped tank you can almost not even tell it is unnatural...i find that the best way is to get a 90 degree gradual bend and use it in a corner..that way you can stack up the substrate in that particular corner and pretty much bury everything besides the openings (which are coated in substrate so you can't see those much either!

third i would have to go with the driftwood...although i love dritwood covered in java fern/moss and anubias, it is just much easier and less expensive (unless you find your own driftwood) to use the other 2 methods to get the exact look out of the caves that you want, although if you can find the right driftwood, you can have the most natural looking cave ever IMO

4th i would go with the terracotta...of the 4 i would say it is the least natural (although it still looks very good), but is extremely cheap and quick to make...

good luck, theres tons of options...