From the Comprehensive Rules 4.0:

Site cards represent locations in Middle-earth, and are used to chart the progress of the game. Nine sites are placed in your adventure deck. (See building your deck.)

Site cards have a dark compass in the upper left corner. This symbol is used on sites from the Shadows expansion set onward, differentiating them from sites found in previous sets (which use a different compass symbol, and may also use a block symbol).

If your fellowship moves to a site that has not been played yet, one of the Shadow players must place a new site on the adventure path. (See moving your fellowship.) To determine which player, look at the site you are moving from. Each site has an arrow at the bottom center of the card. This indicates who is to play the new site, with → meaning the Shadow player to your right and ← meaning the Shadow player to your left. In a two-player game, there is only one Shadow player at a time, so that player always plays the new site.

That player looks through his adventure deck and chooses any site to play as the next site. It takes on the next consecutive number on the adventure path as its site number. It also takes on a region number. Exception: See format.

You may play a copy of a site on the adventure path even if an opponent’s copy was already played as an earlier site and is still active. The copies are treated as different sites, with each
given a different site number.

Some cards allow a player to play the next site on the adventure path at times when the fellowship is not moving. These may be used even when the next site is already there. In such cases, the new
site replaces the old one; put the old site back in its owner’s adventure deck. The new site takes the same site number the old site had, so that there is always only one site 1 in play, one site
2, and so on. When a site is replaced, all cards played on or stacked on the old site are moved to the new site.

Shadow players may take control of sites on the adventure path and the Free Peoples player may liberate controlled sites. Various card effects refer to these controlled sites as well.

See also culture, kinds of cards.