Maintenance day

Took the chain off the mountain bike and soaked it in chain cleaner for a while as it was starting to get really dirty again. Something's loose at the front, I can wobble the pedals from side to side by about half a centimetre. Took the pedals off, crank arms were still wobbling, tightened the crank arms, still wobbling, so I'm guessing it's time for a visit to the bike shop. I'm guessing it's something in the bottom bracket, but I don't have the tools to take it apart and see, and even if I did I don't think I'd want to take it apart and find it was so worn I couldn't put it back together in usable form!