1 BORDER USR 7766^0:
 POKE 23693,7:
 DIM m(999):
 LET e=INT (RND*5)*64+415:
 FOR r=0 TO 9:
 PRINT r;"0%":
 FOR c=33 TO 47:
 RESTORE :
 READ n,p,z,s,m(66),m(e):
 POKE n*m(p),23:
 LET y=INT (p/64):
 LET x=p-y*64:
 LET w=INT (RND*4):
 LET d=32*((10>y)*(w=1)-(1<y>w))-(w=2)*(x>2)+(w=3)*(x<30):
 LET p=p+d:
 POKE n*(m(p+d)=z),8+z*15:
 LET d=2*d*z-d:
 LET z=1:
 LET m(p)=1:
 LET p=p+d:
 LET m(p)=1:
 POKE n,11:
 NEXT c:
 CLS :
 NEXT r:
 PRINT AT 0,0;"Steps:";r-10:
 FOR g=1 TO 5:
 LET k=s+CODE "d$CED"(g)-68:
 POKE 22528+k,11*m(k)+g:
 NEXT g:
 LET x=CODE INKEY$-48:
 POKE n*(x<0),31:
 LET d=32*((x=6)-(x=7))+(x=8)-(x=5):
 LET d=d*m(s+d):
 LET s=s+d:
 POKE n*(s-d<>e),25+(d=0):
 BORDER 2:
 DATA 23620,r*64+2*c,0,580,1,1

You are the Dutch operator of the PATHFINDER mission on Mars (see here or here) and your plan to attract extra-terrestrial life worked too well! The Martians carried the probe through the canals down to their underground city, where they organized a big party and drunk everything available. Hours later, you finally restore contact with the probe, which was abandoned deep inside the Martian caves. Now you must guide the probe and find a way out of the underground tunnels, so NASA can recover its footage of life on Mars!