Start with the loop that is actually confirmed
Nuke Your City is a tycoon-style Roblox simulator: grow the nuke, launch or cause destruction, buy machines and upgrades, then work toward rebirth and research.
For nuke your city how to level up fast, start by redeeming or checking BOOM, then put your early time into machines and upgrades that help the next launch cycle. Public code sources agree BOOM exists, but they disagree on the exact Playtime Points amount, so this guide keeps the reward wording broad until it is verified in game.
The official Roblox description confirms that explosives grow offline. If you just came back, open the game and inspect your current progress before buying anything. That check can change whether the next useful move is another machine, a direct upgrade, or saving for the rebirth path.