If you have 6 hours to spend in Melrose, there are several things that you can do. One of the most popular attractions is Melrose Abbey, a ruined monastery that dates back to the 12th century. It's worth spending at least an hour here, exploring the ruins and learning about the history of the abbey.
If you're interested in historical architecture, you could also visit the nearby Harmony House. This 16th-century building is beautifully preserved and has a fascinating history. It should take you around 30 minutes to see everything here.
If you enjoy walking and outdoor activities, you might like to take a stroll along the River Tweed. There are several walking routes around Melrose that offer stunning views of the countryside. You could also visit the nearby Eildon Hills, which offer a more challenging hike but also have some incredible views. Make sure you're wearing appropriate footwear and clothing and allow at least 2 hours for the walk.
Finally, if you're interested in history and literature, you might enjoy a visit to the Darnick Tower. This tower dates back to the 15th century and is said to have inspired Sir Walter Scott's novel, "The Betrothed." It should take you around 30 minutes to explore the tower and its surroundings.