Make a General Trigger and draw it on the ground. Go into its properties and edit its ONENTER property and then use a script like the one below. The script below describes the room the player character has just entered, and it functions because the character crosses a trigger event which the character has no choice but to cross (since the trigger is purposely designed that way to ensure the description is given to the PC).
NOTE[]
I did not come up with this script. I found it on a website a year or two ago and it had no information about the author. If I knew who he/she was then I would give proper credit
void main()
{
object oTriggerer;
oTriggerer = GetEnteringObject();
SendMessageToPC(oTriggerer, "You've entered a natural cavern about 40 feet across and about 25 feet high in the center.");
SendMessageToPC(oTriggerer, "The floor is flat and very dusty with a few scraps of dry vegetation scattered.");
SendMessageToPC(oTriggerer, "There are numerous tracks visible in the dust. Most are those of small animals, but a number of larger,");
SendMessageToPC(oTriggerer, "human-like tracks form a clear path from the entrance to a dark exit to your right. Another exit");
SendMessageToPC(oTriggerer, "on the opposite side of the cave, appears unfrequented.");
}