Turtles All the Way Down
Batch, 256 bytes

@set i=echo 
@%i%off
set u=
for /l %%j in (2,2,%1)do call set i=%%i%%  
set/af=%1^&amp;1
if %f%==1 %i% __&amp;%i%/,,\o&amp;set u=__
for /l %%j in (2,2,%1)do call:l
exit/b
:l
set i=%i:~0,-2%
%i%  _%u%_
%i%o/,%u%,\
%i% __%u%__
%i%/,_%u%_,\o
set u=__%u%__


Note that line 1 has a trailing space and line 4 has two trailing spaces. i therefore contains an echo command with the appropriate amount of indentation for each turtle. Meanwhile u contains the number of underscores in alternate turtles. A leading odd turtle is special-cased and then the rest of the turtles are output in pairs.