For about nine months now we've been working on an application for a customer to manage their construction projects. IT IS AN ABSOLUTE MONSTER! I kid you not. We are about 80% done and the current table count is 32. 32 tables! As the architect of the solution I found it very hard to get my head around how this would all logically fit together. The application basically tracks a project's progress against the quote. Remember we're talking construction projects here so some of the numbers get pretty big (like hundreds of millions). Also the number of items to manage in a quote are in the thousands. Then each month we do a forecast on each item to determine the project's position. Each month thousands of rows are created for each projects as a snapshot of the project's state.
This is easily the most difficult project I've been involved in. I love a good challenge but there were times when I doubted what the client wanted was even possible.