Visiting Frankfurt in April - looking for help with recommendations

3 friends & I are visiting Frankfurt during April. We’re are doing some research into what we can do / visit while in the city. I thought I’d ask if anyone has any recommendations?

Also while being in Germany, I wanted to know if anyone can recommend a bar / pub that offers beer servers in steins (1ltr / larger) within the city. We are staying quite central. (I ’m aware of this city being more apple wine focused, but while in Germany I wanted to try this)