Realistic lava? Educated insight requested.

[Talonos]

I want to have a lava room in a dungeon I'm making. Thing is, most RP supplements just treat lava the same way videogames treat it: liquid that deals a lot of damage if you step in it. I want mine to be a little more realistic.

I'm picturing a room with a lake of lava in it with the top open to the sky (hundreds of feet up). The heat from the lava generates a strong updraft, so the tunnel leading to this room is windy (because the air needs to come from somewhere, after all! Finding the "source" of the wind uncovers the other exit to the dungeon...)

I've heard real-life lava is hot enough you can't get within a few dozen feet. Would the convection from the updraft be enough to have a lake of lava in a room and you be able to be in that room? Or would there be enough "radiant heat" to bake anything that comes close?

I've heard Real-life lava emits poisonous gas. Is this true? What sort of gas?

I've heard real-life lava cools more quickly than one would expect. Is this true? What sort of geologic activity would be necessary to keep the lake of lava an actual lake?

Also, there's the problem that if lava is molten rock, then why isn't the rock around the lake melting? Would it be realistic for the surrounding rock to have a higher melting point or something? How could I justify that?

Thanks. GURPS attracts some highly educated folks. I've rarely asked a question in here without having somebody able to point me in the right direction.