Lublin has plenty of historic sites, landmarks and tourist attractions worth seeing.
Here is a short list of places you absolutely must see to understand the history of Lublin.

The Castle Hill:
The Holy Trinity Royal Chapel
The Lublin Museum at the Castle
Castle Tower

The Old Town:
Townhouses in Market Square
The Crown Tribunal
The Lublin Underground Route
The Dominican church and monastery
Po Farze Square
The Trinitarian Tower

The City Centre:
Lublin Cathedral
Krakowskie Przedmieście
Litewski Square

Other places:
The State Museum at Majdanek
The Open Air Lublin Village Museum