Linden Grove, a former country estate on the outskirts of Millford, was established in 1823 and later repurposed as a municipal park. Estate inventories list a network of utility shafts used for coal and water distribution, and an 1887 survey map sketches a “pergola aisle” that some historians interpret as a concealed passage. Contemporary newspaper notices from the 1920s also reference “restricted corridors” accessed only by staff.
Physical investigation in 2021 by the Open Ledger’s heritage team identified three sealed doorways along the east lawn, consistent with the older schematics. However, ground‑penetrating radar yielded ambiguous reflections, suggesting either collapsed voids or modern utilities. No definitive photographic evidence of an intact passage exists, and the park’s current safety regulations prohibit unsupervised entry, limiting direct verification. Researchers also consulted archival photographs from 1932, which show remnants of a concealed stairwell now obscured by mature oak roots.