As your baby is starting to explore putting objects together, and inside each other now might be a good time to get some simple wooden blocks. Blocks are a toy your baby can use in different ways as they grow and develop and for now, they might just be interested in picking them up and having a good look at them.
You could show your baby how you can place blocks on top of each other, and then knock the tower down again. Give them time to touch, hold and move the blocks and watch as they begin to place them together or try to put them on top of each other.
Stacking blocks is quite a tricky physical skill so your baby might need lots of practice before they can build a tower.