FINAL RESULT !!!
Starting out with simple plastic boxes:

Cutting 2 boxes up and gluing them together with aquarium silicone:

Checking the fit in the 160 ltr aquarium:

Modelling the cave with Makemake aquarium concrete:


Decorating with small twigs and gravel:

Close up of the decoration:

Checking the fit again:

Attaching more roots with silicone inside the cave to simulate roots penetrating the cave-roof/layer:


And a nice result, I think:


Applying the 2./decoration layer - also creating a small wall to keep in the aquarium soil I intend to put on top:

On the overhang I intend to plant/attach mosses and opened-up algae-balls:

I saw on Youtube that you can attach moss with superglue, so why not with silicone:

Ready for action:

Here I fill the biggest voids with filter material:

..and then cover everything with Tropica aquarium soil:

A quick "dry-run" of my intended aquascape:

Here I attach the moss strips to the overhang with silicone, and start filling up with water:

Tying mosses on to roots with ultra thin and strong fishing elastic string:

And here the tank is beginning to take shape, with mosses fitted strategically:

Foreground plants, Eleocharis acicularis "mini", ready for planting:

Planting:

Hemianthus callitrichoides "Cuba" & Eleocharis acicularis "mini":

Attaching taller plants like Microsorum pteropus "narrow" to articficial, sinking piece of root:

Now is the waiting game, letting the plants grow and spread...:

The plants have grown (along with all sorts of algae), but it starts looking better. Also, I have finally put some fishes in there:

FINAL RESULT:
