impressive
/ɪmˈprɛsɪv/
adjective
adjective: impressive
evoking admiration through size, quality, or skill; grand, imposing, or awesome.
"an impressive view of the mountains"
For this context there was either any weapons and/or some or possibly all were of high quality, such that the cache would impress either the police, or for example a weapons collector/expert.
it is always best for provide much more context = more of the full text.
Also for writing you could explain and give details as to why the cache is impressive.