I'm considering a day trip to Brussels from Amsterdam while my sister attends a conference. 1. Is this safe for a solo female traveler? 2. What is there to see and do in Brussels on a day trip? Thank you in advance for your suggestions.
Safety - just like any other big city, no worse than Amsterdam.
One problem with doing a day trip to Brussels is that the most interesting sites are spread quite widely around the city. My personal suggestion would be to see the Grand Place, which should not be missed, and then head to the southern area of the city and see the Horta Museum and some of the other art nouveau houses in the streets around. But it would help if you said the type of thing that interests you.
I have been in Brussels many times on my own as a female traveler, and have never felt any safety concerns, or at least no more than I feel in any large city. Just stay around the area from the Central Station to Grand Place or St. Catherine. My favorite visit is the Musical Instruments Museum on the hill near the Central Station. Then walk down the street to the park at Place du Petit Sablon. Immediately across the street behind the church, stop in at Wittamer chocolate shop. Divine!
Brussels is safe for a solo traveler. You can spend a day walking around the center eating, shopping, people watching.