As of Spring '18 release, Recycle Bin is still not exist Lightning, vote my idea Lightning Experience - Recycle Bin to get this delivered in coming release.
However, if Recycle Bin is a must, and you can't wait if they will be made available in the future release, here is the workaround.
1. Access to page /search/UndeletePage
If your Lightning URL is https://ap1.lightning.force.com/one/one.app#/home change this to https://ap1.lightning.force.com/search/UndeletePage
Once you access the page, you will see Recycle Bin as in Classic. Note, this is only applicable to users allowed to switch back to Classic. When you finish and click any tab or record, it will bring you back to Lighting.
2. Add to Lightning Component
It would be troublesome to communicate to all users to bookmark that page.
Adding the "Recycle Bin" link to a page will be much easier, including for training and writing manual guide.
With a simple Lightning Page editing, add a Rich Text component, in my case, I add it to the Home page.
Additionally, there is a 3rd app in AppExhange to add Recycle Bin in Lightning https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3000000Dq7VmEAJ
Reference: Lightning Experience - Recycle Bin