Dragon, a massive wide cavern, high ceiling, smooth walls from the dragon body scraping the sides, coins, jewels, precious metals, weaponry and other riches scattered on the floor and piled up in adjoining chambers, heat vents, fissures, stalactites and stalagmites, nesting area made from branches, fresh leaves, melted gold coins to form a bowl to keep the eggs (clutch) warm during absences, bones, skeletons, skulls, spoiled meat, ragged clothing from past dead adventurers, hoarded items of a magical nature (scepters, crowns, tiaras, rings, amulets, staffs, potions, gemstones, cursed artifacts, robes, knives, chalices, etc), old discarded dragon scales on the floor, egg shells, crumbles of rock, boulders, debris, scorch marks on the walls and floor, cracks in the wall or high ceiling, weaponry and smashed, splintered shield the dead left behind, fire, smoke, cliff ledge
The crash of water and waves (if located on a cliff face on the ocean's edge), powerful inhaling and exhaling that reverberates throughout the chamber, the scuff of a foot, the drag of a tail, knocking over a stalagmite with a crash, a metallic slide of metals and coins from sorting through treasure piles, a rumbling snoring sound, the crackle of branches as something large settles on the nest, scraping noises as the dragon rubs its side against the wall for itchy relief, the flutter and flap of wings settling and adjusting, angry bellows, the roar and crackle of fire, noises and shifting echoing throughout the cavern, soft footsteps in the dust, sneaking toward the treasure hold, the crack of eggs breaking, the squawk and cry of new draglets
Fire, blood, metal, char, brimstone, the sea, salt, hot stone, musty air, rotten food breath, death
Sour tang of fear, sweat, dry mouth...don't think you want to stop here for a picnic
Rough handhold climbing up to the lair entrance, stone digging into knees, cutting hands, scraping legs and arms, inside: taking careful steps, picking your way across a floor littered with bones, rock and riches, careful not to disturb anything, pausing to wipe away droplets of sweat, chest tight from forced light inhales and exhales, pain in the ankles and legs from holding a stiff position at the slightest sound, reaching for a jewel or sword, wincing and gritting teeth as you attempt to pull it soundlessly toward you, dropping small baubles and coins in pockets, constantly glancing up and this way and that as you collect for fear of the dragon awakening or returning, drawing a weapon free from a scabbard to do battle, the drag of armour and a shield pulling at arms and shoulders, heartbeat straining, panicked running at being discovered, The pain of skin burning, hair sizzling, crushing pain of a talon or tooth piercing chest, a wing bashing into you, throwing you against the wall, or giant foot crushing air from lungs, the final exhale of death
--The words you choose can convey atmosphere and mood.
With each exhale, Ceron's face burned and came close to blistering, but he gritted his teeth and stayed focused on the key resting just beyond the sleeping dragon's blood-splattered claw. Two more steps and he would be able to free his son, shackled in the antechamber by the giant beast for daring to wander too close to its lair.
Harland stood outside the cave mouth, refusing to go in. Something terrible was inside, for not only did a chilling rumble sweep down the passage toward him in a steady beat, it carried upon it a stench that made him wonder if the mountain had swallowed a demon and it lay decomposing within its stomach.
--Similes and metaphors create strong imagery when used sparingly.
Example 1: (Simile)
Rubies and emeralds dotted the pile of coins like sweet currants decorating a cake.
Example 2: (Metaphor)
I glanced back at mouth of the cave and the unblemished blue sky beyond. The realization that this would be the last time I drank in such a sight was a heavy shield to carry, yet at least the burden was mine alone.