Tour the castle! There are various options for guided and self-guided tours, with tickets priced at $23 per adult.
There is a parking lot just beyond the Castle in the Clouds gatehouse entrance on the right. There are several hiking trails that can be accessed from here. The Bald Knob Trail (our favorite) is a lovely ~2 mile easy-moderate hike with stunning views of the lake. If you've never done it before, make sure you don't accidentally stop halfway up! If you're still within the tree line you're only halfway there! There is also the Brook Walk that takes you down from the Castle parking lot following seven beautiful waterfalls, and is a very relaxing experience.
The Mount Washington is a historic boat that crosses the lake multiple times per day. They also offer sunset dinner cruises!
If you are staying in the Mills Falls hotels, definitely take some time to explore Meredith. There are so many cute shops, restaurants, and scenic views to enjoy.
This is a historic town on the lake that touts itself as the first vacation destination in the US. Very cute with lots of restaurants and shops on the water.
This is a great place to kill a few hours, and a great way to spend a rainy afternoon if you have little ones with you. There are plenty of arcade games, bowling lanes, and mini golf. There is also a go-kart track across the street.
Make sure you get to spend some time on or in the water, whether you just go for a swim, rent some kayaks, or get a chance to rent some jet skis or a boat!