Longwood Gardens is located in Kennett Square, Pennsylvania, and is about a 45 minute drive south-west of Philadelphia's center city. They've got more than a thousand acres of land you can stroll through outside, and have multiple conservatories (with 4 heated acres of space) to enjoy inside. Every time I've been there, which is three or four times now (a lot considering I live ~3,000 miles away), I've found something new and beautiful to enjoy.
On this past trip it was pretty cold, at least for us California pansies, but we still perused many of the trails before heading inside the greenhouses. They've planted more than 2 million bulbs throughout their grounds, and so most places you looked bulbs were starting to pop up and bloom.
They have some very nice manicured outdoor gardens; the one in the picture below is the main fountain garden. The fountains were turned off while we were there this time, but judging by the picture on their homepage (which is currently of the same garden), they're spectacular.
If you wander through a forest on the grounds you're rewarded with this view of a serene meadow, which you can hike through. We didn't walk through it this time due to the temperature, but have on prior trips and it's a neat area.
But naturalized bulbs and pretty views outside aren't the only reason to go to Longwood; there are also tremendous heated conservatories that house an amazing variety of plants. They have greenhouse areas that specialize in bonsai, palms and cycads, orchids, roses, ferns, Mediterranean climates, and tropical climates, to name a few. Walking into the greenhouses is just amazing, as you're presented with views like this:
Now if only I could get them to build a Longwood Gardens 2 in California, complete with the moist climate and seasonal variation in environmental temperatures, living in California would be complete.
Note: these pictures were taken on April 3, 2004.