Hi there,

I'm already doing some outdoor biking which allows my lower body to be
muscled up. Now I'm searching for pleasant sports to muscle my upper
body, with the following conditions: it should be a sport that can be
done alone at anytime of the day (versus group or duo sports like
tennis, soccer, etc) or indoor (video game that is very sporty).
some examples I have in mind are climbing (but that is not necessarily
easy to do anywhere unlike biking for the lower body). (swimming is
ruled out as it's a n indoor sport)

upper body=arms, abs, chest

Many thanks
Ben

I think the outdoor qualifier will get you very few responses for
upper body building.

Disc Golf is a great one, although not as much muscle building as you
might like.  www.pdga.com   There is probably a course near you.

I think cycling is good for the upper body, because you are supporting
much of your weight.

Learn to walk on your hands.  It is not really difficult, and you can
do it any time and place  - and when you get good at it, you can wow
people at the beach or win bets that you can do it for one minute. 
However, I wouldn't suggest taking bets of beers in a pub.

Despite the last, this is a serious suggestion.

Thanks a ton to all suggestions so far. 

I guess walking on hands is quite original and do-it-yourself-anytime
but the issue is that you certainly can't do it without being widely
observed! (which can be turned into an advantage in some circumstances
as said!). :))

Now, "outdoor" is a subcategory of fun... that's why I said "outdoor"
or if indoor it must be fun to do and not the usual look at the wall
type of indoor gymn stuff. so, outdoor sport/game or indoor (video)
game

I recently played a new game I saw displayed at Best Buy...  It's a
guitar game that looked and sounded real cheesy at first, but i loved
it after trying.

Basically, you are holding a guitar (a controller guitar that has 4
buttons instead of strings and a strip at the head where you strum)
and the point is to play the guitar lines to songs by pressing the
right button and strumming at the right time.  The screen tells you
when/what to play and the game makes the notes as if you had played
them for real (even the bad notes you play).  I highly recommend it,
it's loads of fun.  And after 4 songs I was feeling as if I had worked
out a bit  **holding guitar up, strumming, pressing buttons, jamming.

Guitar Hero, Guitar Hero 2

Swingball, tennis and golf are great for your upper body and the mucles in arms.