The elevator can be found to the left of the big snake that's sitting on the tree trunk.
Achievement Walkthrough in 12 minutes. Timestamp (4:40) Lookout tower Achievement.
Timestamps:
(0:20) Arround the Burrow L1
(3:00) Encyclopedist Ach
(3:25) The Forest L2
(4:40) Lookout tower Ach
(7:05) The Pond L3
(7:50) Sailor Ach
(9:15) The Garden L4