Borough Market - The Best Day Out in London, hands-down

I get it that visitors to London have a few sights that they need to see to check the box - Westminster Abbey / Big Ben, Buckingham Palace, Tower of London... there's also likely a few quintessential English foods and drinks that need to be tried such as fish & chips, a Sunday roast, and some English lager.  But I'd be hard-pressed to think of a better day out in London than making a trip to Borough Market.  A food market, yes, but like no other I've seen before - vendors from all over Europe set up stalls here and it's open to the public Thursdays, Fridays and Saturdays (check the hours before you go).  I recommend getting there on Saturday before 11am or be prepared for some serious crowds.  There's the direct way of doing Borough Market (get to London Bridge Station, and walk to market), or the recommended indirect way of doing it - taking in some great views of London and seeing some parts of the city that could otherwise be missed.

So here's the recommended Best Day Out in London, rated as such by sample size of 1.
Get to Waterloo Station and then head to the Thames.  Stay on the southbank and head East along the water.  You'll pass by the Royal Festival Hall (you can pop in for a takeaway tea or coffee if needed), then the National Theatre which hosts outdoor theatre/art installations from July-September in an area called Watch this Space (http://www.nationaltheatre.org.uk/wts), eventually you'll pass a lovely alfresco secondhand book store - nice for a brief wander.  Continue walking along the bank, taking in sights of London to the north such as St Pauls.  You'll eventually pass the Tate Modern and Shakespeare's Globe Theatre...  the Thames path ends at a nice pub called Anchor Bankside.  Follow all the rest of the people weaving their way down a road that continues eastward... after you pass London Dungeon, take a right and you are at Borough Market.  It might not look like much from that first angle you're entering - but 2 minutes of exploring it will start to enthuse the senses!
I could write several entries about all of my favourite stalls - but here's some pics I took on my first visit there to whet your appetite.

You can sample some prepared foods there or take some of the fresh meats, seafood, cheeses, and produce home for a scrumptious meal!  Once your senses are satiated, you can head back to the pub on the river (Anchor Bankside), grab a beverage and sit on the water for a bit of relaxation.  Once refreshed, head back along the Thames path (the way you came) until you get back to the Tate Modern  You might want to pop in this museum as much of it is free and worth a look, even if to ponder how some pieces made it into the permanent collection.
Next, walk across the Millennium Bridge, called the wobbly bridge by locals as it was improperly built the first time round and wobbled to the point that they had to close it down for some years before re-opening to the public.

You might wish to pop into St Pauls for a look - they do charge you to have a wander but it's worth it if you brave the steps to the top for a stunning panoramic view of London.
Get to the Thames path along the northbank and now head West until you get to Embankment Tube Station. Walk through it and head up the small road, typically filled with pedestrians and the occasional car.  On your right, look out for Gordon's Wine Bar - London's oldest wine bar. After braving the narrow steps down, head to the bar for a glass of wine and then try hard to get a seat in the "cave" - you will know it when you see it.  After 3pm on any day, the cave tends to fill up with people - but if you lurk near one of the entries to it, you shouldn't have to wait too long for a seat - it's well worth the wait (and the shame of being a lurker)!

And this concludes the Best Day Out in London - after all that walking and wine drinking, a siesta is highly recommended... no, we're not in Spain, but with places like Borough Market and the atmospheric Gordon's, you won't feel like you're in London either.