For a real sandbox?

You set it up so that you have say.. a celestial outpost either on the outskirts of the 9-Hells or actually somewhere in a "protected realm" within the Nine Hells. And you detail the terrain outside the area.

The Outpost has some kind of protection (perhaps an ancient angelic Aegis or something..) that keeps it from being just overwhelmed automatically as soon as some really big Pit Fiend takes notice. Maybe it's hidden, or maybe it moves or gies invisible.. or maybe it's really just nearby a gateway. Or perhaps the outpost itself is on the edge of a spreading taint where hell has started to bleed over into another area of the prime material.

Detail the Outpost as a starting town, except instead of a town, it's a fortress. A forward operating base in hostile territory.

Detail the surrounding/neighboring hexes as "hell hexes" or whatever.

The characters are adventurers who are taking part in this whole forward operating base situation. Adventures could involve capturing territory, escorting supply shipments in and out. Striking at key infernal strongpoints and ambushing enemy commanders, perhaps seizing artifacts or whatever.

It doesn't make that great of a sandbox because the situation (your characters are in hell) is so dire, you can't just "casually adventure around". Well, you could.. but most players would not be looking at the situation casually.

Quote from: Abyssal Maw;376851For a real sandbox?

You set it up so that you have say.. a celestial outpost either on the outskirts of the 9-Hells or actually somewhere in a "protected realm" within the Nine Hells. And you detail the terrain outside the area.

The Outpost has some kind of protection (perhaps an ancient angelic Aegis or something..) that keeps it from being just overwhelmed automatically as soon as some really big Pit Fiend takes notice. Maybe it's hidden, or maybe it moves or gies invisible.. or maybe it's really just nearby a gateway. Or perhaps the outpost itself is on the edge of a spreading taint where hell has started to bleed over into another area of the prime material.

Detail the Outpost as a starting town, except instead of a town, it's a fortress. A forward operating base in hostile territory.

Detail the surrounding/neighboring hexes as "hell hexes" or whatever.

The characters are adventurers who are taking part in this whole forward operating base situation. Adventures could involve capturing territory, escorting supply shipments in and out. Striking at key infernal strongpoints and ambushing enemy commanders, perhaps seizing artifacts or whatever.

It doesn't make that great of a sandbox because the situation (your characters are in hell) is so dire, you can't just "casually adventure around". Well, you could.. but most players would not be looking at the situation casually.

Op says only 1 PC....

I say you start the PC as he falls through a dimentional rift into Hell and let the fucker fight his way out.  Personally  would run Hell more like the Vertigo interpretation in the Lucifer comics, ie a series of diverse realms constantly striving for control, so the Paladin might well end up making some unusual allies in order to fighter a greater evil.
Of course it would be tough for a single PC in such hostile territory so I would give him some sort of artefact to give him a chance or apply some sort of formal social rules to the Lawful evil Hell planes. A rule of Hospitality for example might mean that he is entilted to a degree of protection from some quarters, of course means that he needs to not be Lawful Stupid

Use the "Reason To Go Adventuring" rule - Nobody sane (Aside from a PC ) goes adventuring with just an ordinary sword, armour and shield.

Or in other words, give him some serious gear, so he stands a chance.