Core Keeper

To go from level 0 to level 100 you need 498768xp. You gain one xp every 0.95 tiles. It's pretty long to max but also is pretty easy. The faster you run the more distance you make the more xp you get.

To power level it in about 8hours of none stop running (it should take you less because you are not level 0 in running) first you will need to choose if want to do it the idle way or the fast way.

Idle : you can create a long tunnel facing your spawn point (a bed or the core) and make your caracters go straight to the left or right after reaching the end of the path make him die whit trap or lava. The longer the path the faster the xp. Note that if you dont have an turbo controler and do the rubberband method the game will make you actually idle and stop after 10minute. Also of you are playing hardcore dont even try to die bruh.

hard way : boost your speed whit equipement. You can buy "cave coffee" from a vending machine inside the metropolis or break it to have it in your basse.
Or just us the speed build that a give inside the 200% speed achievement it's pretty time consuming to farm for all of the item inside the build but if you dont want another 20hours of gameplay only walking in a straight line well go farm the loot upgrade it and run in a long tunnel.

Whatever you deside to do you need to make a monster proof path because monster will slow you down and can damage your armor so put wall on both side of the tunnel and rail so that no ennemis or plant spawn on it.

It took me 2hours of straight running whit the speed build.

Good luck and dont give up.