Bumpy asphalt floor

Hi guys, after some advice.

Been out to look at a job. Old victorian house.
Bathroom looks like asphalt. About 20mm thick.

It has a huge bump in the floor. About 20cm diameter, raised a good 10-15mm.

Best way of getting rid?

I was thinking possibly knock out. A46, then dpm ssandwich. Or is there a simpler way?

Thanks

 

Tile straight on it then put a bath mat over it afterwards, simple