In the hex is a ruined watchtower, visible for miles around because it always has a fire burning at the top of it, day and night: it's a relic of some clever system of watchtowers that outlived the society that crated it. The ground floor, of heavy, buttressed stonework, is still intact, though the door has long since been broken open. Inside there's a pile of smashed-up furniture and log such as might be used for fireworks, though no sign of a fire having been lit here for some time. There are stone stairs in one corner: the second floor has one or two collapsed walls, so it's open to the elements, but there's still with a coherent floor and stairs rising from the corner of the ground floor into it: there's a trapdoor at the top of the stairs but the wood is weak and splintery. Above, the top floor – the parapet – is mostly but not entirely collapsed, and there are no more stairs to it, though it's not a complicated bit of climbing. The partial floor there of the parapet is stone, not wood, and there's a waist-high wall around it, again now mostly crumbled away.
Now close to the edge of the crumbling floor up there, in a point that would have been the centre when the floor was complete, is a magmin, imprisoned in a cage barely larger than itself made of enchanted, fire-resistant whalebone: the bone not only stops it getting out but also prevents it from returning to the plane of fire.
There are always creatures drawn by the warmth of the magmin around the tower – roll on whatever encounter table you're for this area first, and play that out at the base of the tower. The magmin itself is desperate to return home. It doesn't speak common but it might try and communicate this. It's furious, too, of course.