Sparta Prague is the richest football club in Czech republic with home at stadium Letna in Prague 7 that has capacity of 20.000 visitors. It is currently the second largest stadium in Prague and whole country after Slavia's Eden. There is no official czech national football stadium so Letna hosts often matches of national team as well. Few proposals to make this venue bigger were raised in the past but it was never approved and probably will never be because of the central location and surrounding houses.
You can reach the entrance gate of stadium easily using public transport - it is on the street Milady Horakove about 200 hundred meters eastern of the metro and tram station Hradcanska (green metro line A, trams 1, 15, 18, 25, 56 and 57). In fact there is a tram station called Sparta as well right in front of the stadium. If you prefer walking you can get there from Old town square in about 20 minutes.