One of my favorite museums in London! The building is an old power station along the south bank of the river, easily spotted by the large smokestacks. The main entrance is through the old turbine hall. It's a spectacularly large room that has changing exhibitions designed specifically to fit the space.
The Tate Modern houses a large collection of modern art from around the world. There is pop art by Lichtenstein and Andy Warhol, surrealism by Picasso, impressionist paintings by Monet, and loads more sculptures, paintings, and exhibits from a wide variety of artists. It's spread over several different levels, and picking up a map on the way in is advisable!
My favorite sculpture is the marble statue of The Kiss by Rodin. My favorite painting is one of Monet's canvases on waterlilies. (I sat in front of the painting so long that I had to be asked by a security guard to leave because the museum was closing!)
Whatever concepts you have about art, what it is and what it isn't, will be challenged by the Tate Modern. Some of the other more "modern" art goes a bit over my head. The installation and concept pieces aren't really my cup of tea, but there are those that love them and there's always opportunity for discussion! (I heard a couple arguing over one of Rothko's paintings, each vigorously defending their point of view.)
There is, of course, a gift shop where you can purchase prints or postcards of many of the exhibits as well as books and other souvenirs about modern art.
Tate Modern is located on the south bank of the River Thames at Bankside, near Blackfriars Bridge, opposite St Paul's Cathedral and next to the Globe Theatre. Like all British museums, there is no entry cost, except for the special and temporary exhibitions that change seasonally. The cost for those is around £7, and it's cheaper if you have a student card.
It's open until 6 Sunday to Thursday and until 10 on Friday and Saturday.

Tate Modern
Sunday-Thursday 10am-6pm, Friday-Saturday 10am-8pm

This museum houses art from 1900 to the present day. I'm not that into modern art, but I still appreciated a stroll through this free, permanent collection. Again, there are entrance fees for special exhibitions.

My favorite modern artists are Picasso, Monet, and Pollock, and you can find them here. You can also find a painting that looks like a can of red paint thrown at a canvas. Beside it hangs an explanation that reads something to the effect of, "The artist angrily threw red paint at the canvas." Yeah.

Following a visit to the Shakespeare's Globe Theatre, we decided to take in the neighbouring Tate Modern as well. Its home, the vast former power plant now linked to St Paul's Cathedral by the new millennium footbridge across the Thames, seems an implausible home for a major art museum. A remarkable combination of the old and the new, the brick-clad steel building’s central chimney rears 325 feet (99m), only fractionally lower than the dome of St Paul's Cathedral.

The most noticeable change to the outside of the former power station is a two-storey glass construction spanning the roof. It provides natural light into the galleries on the top floors and houses a café offering outstanding views across London. Inside, while three floors offer exhibition space, the cavernous cathedral-like Turbine Hall still exists as a challenge to artists and curators.

In the 5 years since Tate Modern opened, it has become a huge social, profitable, and artistic success. Even more than Shakespeare's Globe Theatre, which opened 100 yards away in 1997, Tate Modern energized the long-neglected Southwark neighbourhood. Art galleries and restaurants have sprung up while renovations and new buildings have appeared.

Tate Modern draws crowds averaging average 11,200 a day, devoted to art but also to hanging out in its large bookstore, its cafes, and its top-floor restaurant overlooking the river. Looking across to St Paul’s Cathedral is like looking at an art show in itself.

Art museums tend to be a mixture of art, pretentiousness, and plain silliness. Examples of the latter: The Tate Museum exhibited a sculpture of 120 firebricks arranged in a rectangular formation and another contained frozen elephant dung. "Embankment," the latest in the Unilever series of commissions to use the cavernous Turbine Hall, falls also, I think, either into pretentiousness or the silly category. By Rachel Whiteread, a British sculptor, it consists of a labyrinth-like composition made from 14,000 casts of the insides of different cardboard boxes, stacked to occupy this cathedral-like space. Some popular art, like "The Dancing Butler" by Jack Vettriano, the most expensive Scottish painting sold so far, on the other hand, is not recognised as art by any art museum.

However, the pop artist Andy Warhol has won through. He raised celebrity to an art form and is now one of the best-known artists of all time and has an entire floor of the gallery devoted to his exhibition. In his self-portrait, Warhol gazes pensively at the camera. His fingers screen his mouth, and his head, which dissolves into black shadow on one side and is barely perceptible in silver on the other. This mechanically reproduced silkscreen not only removes evidence of the artist’s touch but also disguises his emotional presence. What is missing in Warhol’s flat garish reproductions is as important as what is there.

Along with the various free exhibitions, others with an entrance fee were also running. These included Jeff Wall: Photographs and Henri Rousseau: Jungles in Paris.

In all, it is an interesting place to visit!

Just across the Millennium Bridge from St. Paul's Cathedral, on the banks of the Thames, the Tate Modern is a perfect example of the proximity of old and new that is so characteristic of London. The museum is housed in an old warehouse that is not much to look at from the outside, but has been renovated inside into a space fit for a well-rounded collection of the world's best modern art. To tell the truth, I sometimes find it challenging to enjoy modern art, and I expected to be somewhat bored when I first visited the Tate. This turned out to be far from the case.

You enter on the lowest level, where you can walk into a huge, open courtyard area that houses interesting rotating exhibits. For example, when I visited, a mammoth several-storied red funnel provided a whimsical greeting. Through a few visits, I found that it seemed best to start out by taking the escalators all the way up to the top floors and work my way down. The galleries are organized by subject matter, theme, or medium (the nudes are all grouped together and easy to avoid with kids), but are also connected, which makes it possible to choose a certain mood or simply wander from room to room. Each floor has sitting areas, some of which incorporate reading and research. There are a couple gorgeous reading rooms overlooking the Thames, as well as a restaurant. The museum offers a varied but quality collection that is stimulating without becoming overwhelming. I would recommend the Tate even to those who typically dislike modern art. Admission is free, so there's not much to lose.

This new museum surely looks ugly from outside. Located in the Southwark, along Thames, it is linked to the other side of the river with Millenium Bridge, which is only open to pedestrians.

Regular exhibitions are rich, with pieces from Gerhard Richter, Paul Klee, Salvador Dali, and many others, but there are also temporary exhibitions here. When I was there, a collection from Kahlo was being exhibited.

The first thing I noticed in this museum was the space. It is so crowded in London, but in this museum, I saw that the average space per visitor is more than in the parks. The museum has a café on the ground floor, but for an excellent view over St Paul’s Cathedral, go to the seventh floor. There is an outstanding restaurant here as well where you can eat modern food, literally.

Entrance to the museum is free, and it is open 10am to 10pm Friday and Saturdays and between 10am and 6pm other days.