To understand the map's content, you need to read all the messages carefully. Then it will be clear why a titan appeared instead of an angel.
They are scared – there is a hint that something might help them – this is understandable.
The key to the library – if you read the signs, it will be clear where it is. Remember games with loot collection – it's not always clear at first ;)
Added 6 minutes later
As for visual bugs, such as passing "through" the gate, I couldn't do anything about it, only remove that part of the model.