Going deeper:

If our adventurous heroes climb ( or - gods forbid - jump) down the hole, they will enter the Mushroom Caves - which are the uppermost level of a lair / underground laboratory.

The creatures inhabiting it grow two different kinds of mushrooms: A "healthy" type, with mild healing properties and a strong scent (which may be used to fool the creatures, whose primary senses are hearing and smell)...

... and a flesh-dissolving, slightly magical type, that requires flesh as nourishment, which the creatures try to provide in the form of unfortunate adventurers.

The "bone disposal hole" near the mushrooms may actually be used to climb down to the lower levels, allowing for a dangerous stealthier approach than the central shaft or the stairs.

A few items that resisted the corroding spores of the mushrooms were considered "special" and placed on a stone slab serving as makeshift altar, along with special "holy" mushrooms.

Looking forward to running this - haven't done "old school dungeons" in a while.

I've started mapping what's under the ruin of Iorek's Tower

The basement looks empty at first glance. There's a prison cell behind the secret door.

A (rather strong) prisoner managed to dig through the wall into the old tunnels behind - and eventually escaped through a hole he covered up with the boulder.

After his escape, he told others of the tunnels and the pit going deeper underground.

These old tunnels might just be the location of a long forgotten treasure my players - and some other people are searching for... at least that's the idea for now.

Will add the other levels as I progress. For now I haven't added lighting to keep the map readable.

That was quicker than expected. :-)

Almost looks a bit too plain without the grid.

Larger versions are in my gallery. And I'm now thinking of what adventures await down the tower's stairs.

Thank you @Loopysue

Using Forest Trail grass. I think the issue is that I tend to cluster multiple patches together (at various scales and orientations), to create organic shapes.

This works pretty well with the dirt patches, but not so much with the grass ones, because they are symbols and the "texture" difference becomes really visible, when the grass patch symbols are not scaled properly.

I'll just make my rounded grass polygons a bit more detailed.

Good luck with your Computer. :-)

Added manual cliff shadows, grass, rock texture around the cliffs, water plants in the creek and more rocks and trees.

Tried using the grass patch symbols. Unlike the dirt patches, I do not like how their texture interacts with the regular grass texture, unless the symbols are scaled just right.

Apart from that, I'm still very happy with the style.