Always check the weather ahead of time and carry protection against animals. (I recommend bear bells and bear spray.)
Summer weekends can be quite crowded and parking may be limited at both Reflections Lake and the Eagle River Nature Center. Also, make sure to bring cash because parking is $5 at the Eagle River Nature Center.
The Eagle River Nature Center hours vary by season. From May until September, they are open Wednesday through Sunday. From October until April, they are open Friday through Sunday. Make sure to check the website in advance to be sure they will be open for your visit.
Both locations can be visited year-round, but make sure to be prepared for winter weather during the colder months.