//On the top of your script
#define PRESSED(%0) (((newkeys & (%0)) == (%0)) && ((oldkeys & (%0)) != (%0)))

//Under OnGameModeInit
Create3DTextLabel("Enter!",0x008080FF,Xpos,Ypos,Zpos,30,0,1);  //Insert the X-, Y- and Zpos of the entrance here
Create3DTextLabel("Exit!",0x008080FF,Xpos,Ypos,Zpos,30,0,1);   //Insert the X-, Y- and Zpos of the exit here

//Under OnPlayerKeyStateChange

if(PRESSED(16)) 
{
    if(IsPlayerInRangeOfPoint(playerid,5,Xpos,Ypos,Zpos)) //Insert the X-, Y- and Zpos of the entrance here
    {
        SetPlayerPos(playerid,Xpos,Ypos,Zpos); //Insert the X-, Y- and Zpos of the exit here
        SetPlayerInterior(playerid,Int); //Insert the Interior of the exit here 
    }
    if(IsPlayerInRangeOfPoint(playerid,5,Xpos,Ypos,Zpos)) //Insert the X-, Y- and Zpos of the exit here
    {
        SetPlayerPos(playerid,Xpos,Ypos,Zpos); //Insert the X-, Y- and Zpos of the entrance here
        SetPlayerInterior(playerid,Int); //Insert the Interior of the entrance here 
    }
}