I want to visit some mature and old-growth forests

Resources for finding old-growth areas

• https://www.OldGrowthForest.net/   [map]
• National Natural Landmarks   [2]
• https://en.wikipedia.org/wiki/List_of_old-growth_forests#United_States
• https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2022.1070372/full — Figure 8

Specific places

• near-ish Chicagoland — spring ephemerals only
  • Pilcher Park Nature Center, near Joliet — "Outstanding spring wildflower displays".
  • Bendix Woods Nature Preserve, past Michigan City — "A spectacular spring ephemeral display of large-flowered trillium".
• Pennsylvania
  • Allegheny National Forest
    • Hearts Content Scenic Area
    • Tionesta Scenic and Research Natural Areas
  • Susquehannock State Forest
• Missouri
  • Big Oak Tree State Park