Hole from bathroom floor thru to exterior, ideas?

[Bazzwell]

Looking over a house this past weekend and saw something that I'd never seen before, let me describe....

Interior:

Second floor bathroom, toilet missing, obvious signs of leakage from the seal. Wood to the left (facing toilet, about a foot back to the wall) rotted to the point of missing completely. Here's the thing I noticed, daylight coming through from the back corner where the wood is completely gone! Maybe a foot wide and from what I could see, three to four inches up. Don't know how far down.

Exterior:

Cement block chimney running directly behind where the toilet in the house was, seems straight and tall. Looking closely you can see where the hole is just behind the chimney but nothing further, can't get closer without a ladder. The chimney seems to serve no function as there is no fireplace and no gas furnace/water heater vent lines.

Any ideas on just what the heck I could be facing? I'm guessing at the least a replacement of a section of bathroom floor, removal of the chimney (if for no other reason than to determine the extent of damage) and some exterior finishing work. My thanks in advance.

[HayZee518]

Evidently there was more than an occasional leak. The major support beams are rotted out compromising the floor's integrity. If you can see daylight - look further into the problem. It probably can be repaired but you need to find some usable wood to nail onto. The basic problem is a leak - somewhere - maybe introducing some water from a bucket will show itself - try it! Got to start someplace.