This is an impressive museum and for the price–free, you can’t beat it. Yes, it’s modern and it has things that you won’t “get” and things that you do “get” but don’t understand why, but the Tate Modern has quite a collection.
Like I’ve found to be the case for a lot of modern art museums (Berkeley, San Francisco, Pompidou) the building is itself a work of art as much or possibly even more so than the contents therein. This is certainly the case with the Tate as I was just blown away by the layout and design of the museum. It’s quite a site to behold.
Much like the National Gallery, the collection of the Tate is vast and holds some of the most well known works of the 20th and late 19th centuries. This isn’t suprising as the Tate is the collection that outgrew the space at the National Gallery to become its own museum. There’s a very cool map outlining everything and also showing you how much area the National Gallery has taken up as time as has gone on.
Beyond the collection, which I’m sure you’ll spend hours and hours in, there is the footbridge that crosses the Thames. Some very annoying (American looking) hippy twits were doing a badly choreographed spacey dance routine in the middle of the bridge, but beyond that, it gives you quite a view of the river, city, and St. Paul’s cathedral which you eventually come to.
It’s quite a day to take on, but I’d recommend grabbing some food beforehand for a light lunch as you go and then starting at St. Paul’s so that you can eat dinner near the Thames in one of the many Asian or Indian places around there. I warn of this, because while there are places to eat around St. Paul’s they’re A) geared more towards a lunchtime, business crowd and B) nothing is open on weekends as we sadly found out.