My house has only one bathroom so ive been tempted to put in a second. The only real option is the basement, but the sewer pipe leaves through the wall about 3’ off the floor. There’s a couple options with pumps, but a lot of negative talk online about it just not being reliable.

Raising the floor seems silly, especially raising it that much, but probably cheaper and more reliable.

Plus I assume this was an old stairway that was walled off in a remodel