Bit of a Pong

And not me! This is my downstairs shower room - the floor level elements. So I went in today and it smells dreadful. I fear that this is linked to the ongoing rat problem (with which I am in despair). On lying on the floor I realise that there are various holes which lead to below the floorboards and Lord knows what else. The pong and indeed a draught are coming in through one or more of these holes. What to do to sort out? Any solutions welcome please.