Well, one interesting Crash Bandicoot and Tawna fanfic I came across had them on a journey to find a lost power crystal. It was really cool as it explored their relationship more deeply, showing how they rely on each other's skills. Tawna's agility and Crash's brute force made for an exciting combination throughout the story.
There are quite a few Crash Bandicoot and Tawna fanfics out there. You can start by looking on fanfiction.net. Some of them might focus on their adventures together in the Wumpa Islands, like how they team up to face new villains or solve mysteries within their colorful world.
Yes, there are some great ones. In a particular fanfic, it was set in an alternate universe where Tawna was the one with the superpowers instead of Crash. The story delved into how Crash had to adapt to being the sidekick and how they both had to deal with new threats. It was a really fresh take on their characters and their relationship.