Things To Do and Restaurants
Poznan is a great city to explore in a couple of days if you want to stay in the city center or there's more to see outside within 20-40 minutes of the city. Poznan was established in 10th century, so there's a lot of historical buildings and castles in downtown. Here is a list of castles and other tourist attractions if you're planning to stay for a couple of days - https://wielkopolska.travel/en/category/castles-and-palaces/
Below is a list of places to see, some are walking distance, some you will need to grab a taxi or Uber (they are everywhere).
Here is a full list of attractions on Google - https://tinyurl.com/yck8a2aa
In Poland you can use your credit card everywhere, Polish currency is called Polish Zloty (PLN) and the exchange rate is around 4:1. For example you'll pay for a beer around 16 PLN (4 USD), cocktails 25-35 (6-9 USD), lunch for one person on the Old Market Square will be around 50-70 PLN (12-18 USD).