There isn't a place more peaceful than the botanical gardens. I've visited the Botanical Gardens of Atlanta, Dallas and the Lauritzen Botanical Gardens which is located in Omaha. The Lauritzen is a tranquil place that has a ton of rare species of plants. This garden did not limit itself to just plants. It also has a beautiful train track that runs through it.
The theme of trains are quite dominant throughout this botanical garden due to Omaha history with the railroad system. There is also other themes such as the rose garden, children's garden and others. My family has visited a few times and we really enjoyed it.
If you live in the Omaha or Area I suggest getting a membership and visiting frequently it is worth it. The Lauritzen Garden is located at : 100 Bancroft St, Omaha, NE 68108