This is probably one of the most pleasant locations in Milwaukee. It's right on the lake, has a huge patio, free outdoor music, and great tea (and coffee I'm sure, I just don't drink coffee). Alterra is located in an old pumping station historic building and they've done a great job preserving it.
I went here for a free summer salsa concert a few weeks ago and had a really great time. The patio was packed, as was the entire lawn area around the building, with everyone set up on blankets and lawn chairs. I'm sure they make a ton of money at this event but I'm glad they don't charge to attend.
I then went back a few days later to join a friend for tea. I tried the blueberry roibus, which was very good but I'm not enough of a tea expert to provide a deeper description. My friend and I also shared the louisiana tofu wrap, which had beans, veggies, and all sorts of goodness, including a slightly spicy dipping salsa.