Václavské náměstí

Overall, this is part of the walking tour.

Parking: n/a
Subway: muzeum (red/green) or Můstek (Line A/green)

Entrance cost: Free
Time cost: Less than an hour

So much history here: (brief list)
On 28 October 1918, Alois Jirásek read the proclamation of independence of Czechoslovakia in front of the Saint Wenceslas statue.
They held many demonstrations here: Prague uprising and velvet revolutions.

The northwest side is the border between Old Town and New Town.
The southeast side has the Statue of Saint Wenceslas and the National Museum.

Yes, as other people mentioned, the square is lined with commercial business shops. Hopefully, it will keep the architecture of the old buildings.

Pro-tip: I would avoid the overpriced, touristy restaurants.

Overall: So, if you can visit, I would highly recommend visiting Prague/Czech during Oct 2018 which marks their 100 year anniversary.
Otherwise, it will continue to be part of the walking tour.