The best project descriptions combine a clear answer to 'what' the project is, with a sense of excitement and passion for it.
What is your project? It sounds like a simple question, but it can be hard to answer! This section should build on the short summary, so make sure that the two are aligned.
First of all you need to be very clear about what it is. You don't need to complicate this. If it's a bridge to cross a stream, then that's what it is! Talk about its specific features and of course, where it will be located. Similarly, if your project is a festival, then think about the kind of details that you would want if you were deciding to go to a festival - where, when, what the entertainment is etc.
Once you've got clarity on what your project is, you want to ensure that you capture the imagination of backers when describing it. A good way to write this section is to imagine that your crowdfunding campaign was successful and your project has been in existence for 6 months. How would you describe it to someone now? That is the tone that you should aim for here. Don't be afraid to be superlative - this is meant to be an exercise in promoting your project after all! What's essential about it? What will it bring to the neighbourhood? When will it be open? Who's it for?
After reading your project description, a potential backer should not have any pressing questions about what it is. They should feel excited and motivated to pledge to you!